How do you adjust the warfarin dose based on INR?

Compare the INR with the target range and change the total weekly dose by a small percentage — usually 5–20% — rather than changing a single day. For a 2.0–3.0 target (UW Medicine nomogram): INR < 1.5 → increase 10–20% (consider a booster); 1.5–1.7 → +5–15%; 1.8–1.9 → +5–10% or no change if recent INRs were in range; 2.0–3.0 → no change; 3.1–3.2 → −5–10% or no change; 3.3–3.4 → hold ½–1 dose, −5–10%; 3.5–3.9 → hold 1 dose, −5–15%; 4.0–4.9 → hold until below 3.0, −5–15%. Then recheck INR in 1–2 weeks.

What does a warfarin dose adjustment chart look like for INR goal 2.5–3.5?

The same rows shift up by 0.5: INR < 2.0 → +10–20%; 2.0–2.2 → +5–15%; 2.3–2.4 → +5–10% or no change; 2.5–3.5 in range; 3.6–3.7 → −5–10% or no change; 3.8–3.9 → hold ½–1 dose, −5–10%; 4.0–4.4 → hold 1 dose, −5–15%; 4.5–4.9 → hold until below 3.5, −5–15%. INR 5 and above follows the same high-INR rules as any target.

How do I calculate my weekly warfarin dose?

Add up every dose you take in one week. 5 mg every day = 35 mg/week. 3 days of 2 mg plus 4 days of 1 mg = 6 + 4 = 10 mg/week. Clinics adjust this weekly total, then spread the new total across the days as evenly as possible, ideally with one tablet strength.

How do you calculate a 10% warfarin dose change?

Multiply the weekly total by 0.10. For 35 mg/week, 10% is 3.5 mg, so a 10% decrease gives 31.5 mg — with 5 mg tablets the closest schedule is 32.5 mg (5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun). A 10% increase from 9 mg daily (63 mg/week) is 69.3 mg/week, about 9.9 mg a day. A 20% reduction of 35 mg is 28 mg/week.

What percent change is going from 44 mg to 47 mg of warfarin per week?

(47 − 44) ÷ 44 × 100 = +6.8%. That sits inside the usual 5–10% step for a slightly low INR. With 1 mg tablets one way to take 47 mg is 7 mg on Mon, Wed, Fri; 6.5 mg on Tue, Thu, Sat, Sun.

My INR is 3.4 and my target is 2–3 — what should happen to my dose?

INR 3.4 is in the 3.3–3.4 row: consider holding ½ to 1 dose and lowering the weekly dose 5–10%. On 7 mg daily (49 mg/week) that is about 44.1 mg–46.55 mg/week — for example 6.5 mg on every day (−7.1%). If your INRs were stable before, CHEST guidance allows keeping the dose and rechecking in 1–2 weeks because 3.4 is within 0.5 of the range.

INR 3.25 on 6 mg of warfarin daily — how much should it change?

INR 3.25 rounds to 3.3, the "hold ½–1 dose, decrease 5–10%" row. 6 mg daily = 42 mg/week, so the new total is about 37.8 mg–39.9 mg/week; with 6 mg tablets the even option is 6 mg on Mon, Tue, Wed, Thu, Fri, Sat; 3 mg on Sun = 39 mg (−7.1%).

Should I skip a warfarin dose if my INR is 3.5 or 3.6?

For a 2–3 target, INR 3.5–3.9 is the row where the nomogram suggests considering holding one dose and lowering the weekly dose 5–15%. On 5 mg daily that means skipping about 5 mg once and moving to roughly 32.5 mg/week (5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun). Only skip a dose when your anticoagulation clinic tells you to.

My INR jumped from 2.56 to 4.4 on 6, 6, 5, 6, 6 mg — should I skip one dose?

INR 4.4 on a 2–3 target is in the 4.0–4.9 row: hold warfarin until the INR is back under 3.0 (often 1–2 days), recheck in 1–2 days, then restart 5–15% lower. Your 6, 6, 5, 6, 6, 6, 6 schedule is 41 mg/week, so the restart dose is about 34.85 mg–38.95 mg — for example 5.5 mg on Mon, Tue, Thu, Sat; 5 mg on Wed, Fri, Sun. A sudden jump usually has a cause (new antibiotic, illness, less food, alcohol), and fixing it may mean the old dose resumes.

What if my INR is 4.8 with a mechanical mitral valve (target 2.5–3.5)?

For a 2.5–3.5 target, INR 4.8 is in the 4.5–4.9 row: hold until the INR is below 3.5, recheck in 1–2 days, then restart 5–15% lower (from 35 mg/week, about 32.5 mg/week). The BNF says vitamin K is for INR > 8 without bleeding, and CHEST advises against routine vitamin K at INR 4.5–10, so most people at 4.8 only need the hold — but valve patients should always call their clinic the same day.

When should warfarin be held based on INR?

Using the UW Medicine nomogram for a 2–3 target: consider holding ½–1 dose at INR 3.3–3.4, 1 dose at 3.5–3.9, and hold until the INR is below 3.0 when it is 4.0 or higher. The BNF says to withhold 1–2 doses at INR 5–8, and to stop warfarin and give oral vitamin K above 8. For 2.5–3.5 targets add 0.5 to the lower thresholds.

Is vitamin K needed for an INR between 4.5 and 10?

Not routinely. CHEST 2012 suggests against routine vitamin K for INR 4.5–10 without bleeding (Grade 2B) — holding one or two doses usually brings the INR down. For INR above 10 without bleeding, CHEST suggests oral vitamin K (2C); the UK BNF uses a lower threshold of INR > 8. Any bleeding needs urgent medical care.

What should I do if my INR is 7.5?

With no bleeding, BNF/BSH guidance for INR 5–8 is to withhold 1 or 2 doses and reduce the maintenance dose — clinics commonly restart 10–20% lower (from 35 mg/week, about 30 mg/week). Call your anticoagulation clinic today and recheck INR in 1–2 days. If there is any bleeding, seek care immediately.

My INR is 1.6 or 1.7 — how do I raise it?

For a 2–3 target, INR 1.5–1.7 calls for a possible one-time booster (1½–2 × the daily dose, e.g. 7.5 mg–10 mg once on 5 mg daily) and a 5–15% weekly increase — from 35 mg/week to about 37.5 mg (7.5 mg on Mon; 5 mg on Tue, Wed, Thu, Fri, Sat, Sun). The INR takes several days to rise, so recheck in 1–2 weeks; first rule out missed doses or a jump in vitamin K intake. INR 1.6 gives the same answer: 37.5 mg/week.

Is an INR of 1.9, 2.1 or 2.2 okay?

For a 2–3 target, 2.1 and 2.2 are in range — no change. 1.9 is just below: if your last two INRs were in range, no change may be needed; otherwise the nomogram suggests a 5–10% increase (35 → 37.5 mg/week). For a 2.5–3.5 target, 2.1 and 2.2 are low (the 2.0–2.2 row, +5–15%).

Does one INR just outside the range always need a dose change?

No. CHEST 2012 suggests that for a previously stable patient with a single INR no more than 0.5 above or below the range, the dose can stay the same with a recheck within 1–2 weeks (Grade 2C). Example: INR 3.2 is just outside 2.0–3.0: if your INRs have been stable, keep 35 mg per week and recheck in 1–2 weeks; otherwise decrease to about 32.5 mg per week (−7.1%).

My target is 3.5 but my INR has been 3.1 for 7 weeks — is that a problem?

Ask your clinic which range your "3.5" means. A 2.5–3.5 range has 3.0 as its midpoint, so 3.1 is in range and seven steady weeks is good control. If your range is truly 3.0–4.0, 3.1 is still in range but near the bottom; any increase should come from your prescriber, usually by 5–10% of the weekly dose.

I take 9 mg of warfarin plus Lovenox and my INR is 2.9 — what now?

An INR of 2.9 is within 2–3, so the nomogram keeps the warfarin dose the same (63 mg/week). For a DVT or PE, CHEST guidance overlaps enoxaparin (Lovenox) with warfarin for at least 5 days and until the INR has been at least 2.0 for 24 hours — your prescriber decides when to stop the injections.

How long does a warfarin dose change take to affect the INR?

Several days. Warfarin’s effective half-life is 20–60 hours (mean about 40 hours, per the FDA label), so a new dose takes roughly a week to reach steady state. That is why clinics change the weekly total in small steps and recheck in 1–2 weeks instead of reacting to every value.

Why are warfarin changes only 5–20%?

The INR response to dose is steep and non-linear, so a modest dose change can move the INR a lot. Small, weekly-total changes avoid overshooting into bleeding range or undershooting into clot risk. The AAFP recommends adjusting the cumulative weekly dose by 10–20% and spreading it evenly over the week.

Can I split warfarin tablets?

Brand Coumadin tablets are scored for halving, and most generic warfarin tablets are too. Many clinics prefer one tablet strength with half tablets on some days to avoid mix-ups. The calculator’s schedule uses one strength in half-tablet steps — pick the strength you actually have.

What do warfarin tablet colors mean?

In the US, each strength has a fixed color: 1 mg pink, 2 mg lavender, 2.5 mg green, 3 mg tan, 4 mg blue, 5 mg peach, 6 mg teal, 7.5 mg yellow and 10 mg white. UK tablets differ: 0.5 mg white, 1 mg brown, 3 mg blue and 5 mg pink. Always go by the milligrams on the label.

Which drugs change the INR on warfarin?

Raise INR: amiodarone, metronidazole, sulfamethoxazole-trimethoprim, fluconazole and other azoles, ciprofloxacin, clarithromycin, erythromycin, regular acetaminophen, thyroid hormone and acute alcohol. Lower INR: rifampin, carbamazepine, phenobarbital, vitamin K and chronic heavy alcohol. Aspirin and NSAIDs increase bleeding without changing the INR. Get an INR within days of starting or stopping any of these.

Can I use this calculator to change my own warfarin dose?

No — use it to understand and double-check the plan your anticoagulation clinic, pharmacist or doctor gives you. Dose decisions depend on bleeding risk, the reason for warfarin, other drugs, diet and recent INR trends. Never change, skip or double a dose without instructions, and seek urgent care for any bleeding.

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Q: What does a warfarin dose adjustment chart look like for INR goal 2.5–3.5?

The same rows shift up by 0.5: INR < 2.0 → +10–20%; 2.0–2.2 → +5–15%; 2.3–2.4 → +5–10% or no change; 2.5–3.5 in range; 3.6–3.7 → −5–10% or no change; 3.8–3.9 → hold ½–1 dose, −5–10%; 4.0–4.4 → hold 1 dose, −5–15%; 4.5–4.9 → hold until below 3.5, −5–15%. INR 5 and above follows the same high-INR rules as any target.

Q: How do I calculate my weekly warfarin dose?

Add up every dose you take in one week. 5 mg every day = 35 mg/week. 3 days of 2 mg plus 4 days of 1 mg = 6 + 4 = 10 mg/week. Clinics adjust this weekly total, then spread the new total across the days as evenly as possible, ideally with one tablet strength.

Q: How do you calculate a 10% warfarin dose change?

Multiply the weekly total by 0.10. For 35 mg/week, 10% is 3.5 mg, so a 10% decrease gives 31.5 mg — with 5 mg tablets the closest schedule is 32.5 mg (5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun). A 10% increase from 9 mg daily (63 mg/week) is 69.3 mg/week, about 9.9 mg a day. A 20% reduction of 35 mg is 28 mg/week.

Q: What percent change is going from 44 mg to 47 mg of warfarin per week?

(47 − 44) ÷ 44 × 100 = +6.8%. That sits inside the usual 5–10% step for a slightly low INR. With 1 mg tablets one way to take 47 mg is 7 mg on Mon, Wed, Fri; 6.5 mg on Tue, Thu, Sat, Sun.

Q: My INR is 3.4 and my target is 2–3 — what should happen to my dose?

INR 3.4 is in the 3.3–3.4 row: consider holding ½ to 1 dose and lowering the weekly dose 5–10%. On 7 mg daily (49 mg/week) that is about 44.1 mg–46.55 mg/week — for example 6.5 mg on every day (−7.1%). If your INRs were stable before, CHEST guidance allows keeping the dose and rechecking in 1–2 weeks because 3.4 is within 0.5 of the range.

Q: INR 3.25 on 6 mg of warfarin daily — how much should it change?

INR 3.25 rounds to 3.3, the "hold ½–1 dose, decrease 5–10%" row. 6 mg daily = 42 mg/week, so the new total is about 37.8 mg–39.9 mg/week; with 6 mg tablets the even option is 6 mg on Mon, Tue, Wed, Thu, Fri, Sat; 3 mg on Sun = 39 mg (−7.1%).

Q: Should I skip a warfarin dose if my INR is 3.5 or 3.6?

For a 2–3 target, INR 3.5–3.9 is the row where the nomogram suggests considering holding one dose and lowering the weekly dose 5–15%. On 5 mg daily that means skipping about 5 mg once and moving to roughly 32.5 mg/week (5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun). Only skip a dose when your anticoagulation clinic tells you to.

Q: My INR jumped from 2.56 to 4.4 on 6, 6, 5, 6, 6 mg — should I skip one dose?

INR 4.4 on a 2–3 target is in the 4.0–4.9 row: hold warfarin until the INR is back under 3.0 (often 1–2 days), recheck in 1–2 days, then restart 5–15% lower. Your 6, 6, 5, 6, 6, 6, 6 schedule is 41 mg/week, so the restart dose is about 34.85 mg–38.95 mg — for example 5.5 mg on Mon, Tue, Thu, Sat; 5 mg on Wed, Fri, Sun. A sudden jump usually has a cause (new antibiotic, illness, less food, alcohol), and fixing it may mean the old dose resumes.

Q: What if my INR is 4.8 with a mechanical mitral valve (target 2.5–3.5)?

For a 2.5–3.5 target, INR 4.8 is in the 4.5–4.9 row: hold until the INR is below 3.5, recheck in 1–2 days, then restart 5–15% lower (from 35 mg/week, about 32.5 mg/week). The BNF says vitamin K is for INR > 8 without bleeding, and CHEST advises against routine vitamin K at INR 4.5–10, so most people at 4.8 only need the hold — but valve patients should always call their clinic the same day.

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INR nomogram · weekly dose · tablet schedule

Warfarin Dose Adjustment Calculator

Quick answer

Warfarin is adjusted by changing the total weekly dose by 5–20%, based on how far the INR is from the target. For a 2.0–3.0 target: INR below 1.5 → increase 10–20%; 1.5–1.9 → increase 5–15%; 2.0–3.0 → no change; 3.1–3.4 → decrease 5–10% (hold ½–1 dose at 3.3+); 3.5–3.9 → hold 1 dose, decrease 5–15%; 4.0 or higher → hold until below 3.0, then decrease 5–15%. Example: INR 3.6 on 35 mg/week → skip one dose, then 32.5 mg/week (5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun). Recheck INR in 1–2 weeks.

Enter today’s INR, your target range and your current dose (same daily dose, a different dose by day, or a weekly total). The calculator applies the UW Medicine maintenance nomogram, CHEST 2012 guidance and BNF high-INR thresholds, then builds a new day-by-day schedule with the tablet strength you have and tells you when to recheck.

For education and double-checking only. Warfarin changes must come from your anticoagulation clinic, pharmacist or doctor. Any bleeding, a fall with head injury, black stools or a severe headache needs urgent care.

Last updated October 2, 2026. Checked against the UW Medicine nomogram, CHEST 2012, AAFP, BC Guidelines and the BNF. · adjust by INR · a 10% weekly change

Warfarin Dose Adjustment Calculator

Enter today’s INR and the current dose to see the nomogram change, any hold or booster, a new weekly schedule and when to recheck.

Try a real example:

INR target range

Today’s INR

Current warfarin dose

mg every day

Tablet strength for the new schedule (halves allowed)

Last 2 INRs were in rangeKnown temporary cause (missed/extra dose, alcohol, short antibiotic)Any bleeding or signs of bleeding

INR 3.6 · target 2.0–3.0 · row 3.5–3.9

INR 3.6 → hold 1 dose, then decrease to about 32.5 mg per week (−7.1%).

Consider holding 1 dose; if a maintenance change is needed, decrease the weekly dose by 5–15%.

Current weekly dose

35 mg

avg 5 mg/day

Nomogram change

−5% to −15%

29.75 mg–33.25 mg/week

Hold / booster

Hold

Hold 1 dose

Recheck INR

Within 1–2 weeks after a dose change

Suggested weekly schedule: 32.5 mg

Mon

5 mg

1 × 5 mg

Tue

5 mg

1 × 5 mg

Wed

5 mg

1 × 5 mg

Thu

5 mg

1 × 5 mg

Fri

5 mg

1 × 5 mg

Sat

5 mg

1 × 5 mg

Sun

2.5 mg

½ × 5 mg

Look for causes: new antibiotics or antifungals, amiodarone, acute alcohol, acetaminophen use, reduced appetite or illness.

How this was calculated

Current dose: 5 mg every day = 35 mg per week.
INR 3.6 with target 2.0–3.0 falls in the 3.5–3.9 row of the UW Medicine maintenance nomogram.
Decrease the weekly dose by 5–15%: 35 mg × 0.95–0.85 = 33.25 mg to 29.75 mg per week.
With 5 mg tablets (halves allowed) the closest even schedule is 32.5 mg/week (−7.1%): 5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun.
Hold 1 dose (one day’s dose, about 5 mg).
Recheck INR: Within 1–2 weeks after a dose change.

Educational tool based on the UW Medicine maintenance nomogram, CHEST 2012 and BNF/BSH guidance. It does not replace your anticoagulation clinic — never change a warfarin dose without your prescriber’s instructions.

How the warfarin dose adjustment is calculated

New weekly dose = current weekly dose × (1 ± percent change). The percent comes from the INR row of the nomogram. For INR 3.6 on a 2–3 target, the row says hold one dose and lower the weekly dose 5–15%: 35 mg × 0.95 to 0.85 = 33.25 mg to 29.75 mg. The closest schedule with 5 mg tablets and half tablets is 32.5 mg (−7.1%): 5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun. The INR is rechecked 1–2 weeks later.

Find the weekly total. Add every dose in one week (5 mg daily = 35 mg/week).
Locate the INR row. Compare the INR with the target range (2–3 or 2.5–3.5) and find its row in the nomogram.
Apply any hold or booster. High rows: hold ½–1 dose or hold until below the upper limit. Low rows: consider a one-time booster of 1½–2 × the daily dose.
Change the weekly dose. Multiply the weekly total by the row’s percentage, typically 5–20% (35 mg − 10% = 31.5 mg).
Build an even schedule. Round to what one tablet strength can give with half tablets and spread larger doses across the week (32.5 mg = 5 mg six days, 2.5 mg one day).
Recheck the INR. Recheck in 1–2 weeks after a change, 1–2 days after a hold for a high INR, and every 4–8 weeks when stable.

Warfarin dose adjustment chart — INR target 2.0–3.0

Used for atrial fibrillation, DVT/PE and most mechanical aortic valves. The example column applies each row to someone on 5 mg daily (35 mg/week) with 5 mg tablets.

INR	Hold / booster	Weekly dose change	Example: 35 mg/week →	Recheck INR
< 1.5	Optional booster 1½–2× daily dose	+10% to +20%	40 mg (+14.3%)	Within 1–2 weeks after a dose change
1.5–1.7	Optional booster 1½–2× daily dose	+5% to +15%	37.5 mg (+7.1%)	Within 1–2 weeks after a dose change
1.8–1.9	Optional booster 1½–2× daily dose	+5% to +10%	37.5 mg (+7.1%)	Within 1–2 weeks after a dose change
2.0–3.0	—	No change	35 mg	Every 4–8 weeks if stable (CHEST allows up to 12 weeks for consistently stable INRs)
3.1–3.2	—	−5% to −10%	32.5 mg (−7.1%)	Within 1–2 weeks after a dose change
3.3–3.4	Hold ½ to 1 dose	−5% to −10%	32.5 mg (−7.1%)	Within 1–2 weeks after a dose change
3.5–3.9	Hold 1 dose	−5% to −15%	32.5 mg (−7.1%)	Within 1–2 weeks after a dose change
4.0–4.9	Hold warfarin until the INR is below 3.0	−5% to −15%	32.5 mg (−7.1%)	In 1–2 days after holding for over-anticoagulation
5.0–8.0	Withhold 1 or 2 doses	−10% to −20%	30 mg (−14.3%)	In 1–2 days
> 8.0	Stop warfarin until the clinic advises	−20%	27.5 mg (−21.4%)	Within 24 hours (repeat after vitamin K)

Rows up to 4.9 come from the UW Medicine maintenance nomogram; 5.0 and above follow BNF/BSH guidance. In the 1.8–1.9 and 3.1–3.2 rows, no change may be needed if the last two INRs were in range.

Warfarin dose adjustment chart — INR target 2.5–3.5

Used for mechanical mitral valves and mechanical aortic valves with extra risk factors. Every low and high threshold is 0.5 higher than the 2–3 chart.

INR	Hold / booster	Weekly dose change	Example: 35 mg/week →	Recheck INR
< 2.0	Optional booster 1½–2× daily dose	+10% to +20%	40 mg (+14.3%)	Within 1–2 weeks after a dose change
2.0–2.2	Optional booster 1½–2× daily dose	+5% to +15%	37.5 mg (+7.1%)	Within 1–2 weeks after a dose change
2.3–2.4	Optional booster 1½–2× daily dose	+5% to +10%	37.5 mg (+7.1%)	Within 1–2 weeks after a dose change
2.5–3.5	—	No change	35 mg	Every 4–8 weeks if stable (CHEST allows up to 12 weeks for consistently stable INRs)
3.6–3.7	—	−5% to −10%	32.5 mg (−7.1%)	Within 1–2 weeks after a dose change
3.8–3.9	Hold ½ to 1 dose	−5% to −10%	32.5 mg (−7.1%)	Within 1–2 weeks after a dose change
4.0–4.4	Hold 1 dose	−5% to −15%	32.5 mg (−7.1%)	Within 1–2 weeks after a dose change
4.5–4.9	Hold warfarin until the INR is below 3.5	−5% to −15%	32.5 mg (−7.1%)	In 1–2 days after holding for over-anticoagulation
5.0–8.0	Withhold 1 or 2 doses	−10% to −20%	30 mg (−14.3%)	In 1–2 days
> 8.0	Stop warfarin until the clinic advises	−20%	27.5 mg (−21.4%)	Within 24 hours (repeat after vitamin K)

Worked examples from real questions

These are the situations people search for most, run through the same calculator.

Situation	Nomogram row	Result
INR 3.6, target 2–3, 40 mg/week (2.5 mg tablets)	3.5–3.9 (−5% to −15%)	Hold 1 dose; 36.25 mg/week (−9.4%) — 6.25 mg on Mon; 5 mg on Tue, Wed, Thu, Fri, Sat, Sun
INR 3.4, target 2–3, 7 mg daily	3.3–3.4 (−5% to −10%)	Hold ½ to 1 dose; 45.5 mg/week (−7.1%) — 6.5 mg on every day
INR 3.25, target 2–3, 6 mg daily	3.3–3.4 (−5% to −10%)	Hold ½ to 1 dose; 39 mg/week (−7.1%) — 6 mg on Mon, Tue, Wed, Thu, Fri, Sat; 3 mg on Sun
INR 4.4 (up from 2.56), on 6, 6, 5, 6, 6, 6, 6 mg	4.0–4.9 (−5% to −15%)	Hold warfarin until the INR is below 3.0; 37 mg/week (−9.8%) — 5.5 mg on Mon, Tue, Thu, Sat; 5 mg on Wed, Fri, Sun
INR 1.7, target 2–3, 5 mg daily	1.5–1.7 (+5% to +15%)	37.5 mg/week (+7.1%) — 7.5 mg on Mon; 5 mg on Tue, Wed, Thu, Fri, Sat, Sun
INR 4.8, mechanical mitral valve (target 2.5–3.5), 5 mg daily	4.5–4.9 (−5% to −15%)	Hold warfarin until the INR is below 3.5; 32.5 mg/week (−7.1%) — 5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun
INR 7.5, no bleeding, 5 mg daily	5.0–8.0 (−10% to −20%)	Withhold 1 or 2 doses; restart about 30 mg/week; call the clinic today
INR 3.0 on 2 mg × 3 days + 1 mg × 4 days	2.0–3.0 (No change)	Keep 10 mg/week
INR 3.2, stable for months, 35 mg/week	3.1–3.2 (−5% to −10%)	Stable: keep 35 mg and recheck in 1–2 weeks; otherwise 32.5 mg/week (−7.1%) — 5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun
INR 1.3 after missed doses, 5 mg daily	< 1.5 (+10% to +20%)	INR 1.3 with a temporary cause: consider a one-time booster, then usually resume 35 mg per week; without a cause, increase to about 40 mg per week (+14.3%).

Weekly dose percent-change chart

New weekly total (mg) after each percent change. Round to what your tablets allow.

Weekly (daily avg)	−20%	−15%	−10%	−5%	+5%	+10%	+15%	+20%
10 (1.43)	8	8.5	9	9.5	10.5	11	11.5	12
15 (2.14)	12	12.75	13.5	14.25	15.75	16.5	17.25	18
17.5 (2.5)	14	14.88	15.75	16.63	18.38	19.25	20.13	21
20 (2.86)	16	17	18	19	21	22	23	24
25 (3.57)	20	21.25	22.5	23.75	26.25	27.5	28.75	30
30 (4.29)	24	25.5	27	28.5	31.5	33	34.5	36
35 (5)	28	29.75	31.5	33.25	36.75	38.5	40.25	42
40 (5.71)	32	34	36	38	42	44	46	48
45 (6.43)	36	38.25	40.5	42.75	47.25	49.5	51.75	54
50 (7.14)	40	42.5	45	47.5	52.5	55	57.5	60
60 (8.57)	48	51	54	57	63	66	69	72
70 (10)	56	59.5	63	66.5	73.5	77	80.5	84

Weekly schedules with 5 mg tablets

Each 2.5 mg step is one half tablet; larger doses are spread across the week.

Weekly total	Schedule
20 mg	5 mg on Mon; 2.5 mg on Tue, Wed, Thu, Fri, Sat, Sun
22.5 mg	5 mg on Mon, Thu; 2.5 mg on Tue, Wed, Fri, Sat, Sun
25 mg	5 mg on Mon, Wed, Fri; 2.5 mg on Tue, Thu, Sat, Sun
27.5 mg	5 mg on Mon, Tue, Thu, Sat; 2.5 mg on Wed, Fri, Sun
30 mg	5 mg on Mon, Tue, Wed, Fri, Sat; 2.5 mg on Thu, Sun
32.5 mg	5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun
35 mg	5 mg on every day
37.5 mg	7.5 mg on Mon; 5 mg on Tue, Wed, Thu, Fri, Sat, Sun
40 mg	7.5 mg on Mon, Thu; 5 mg on Tue, Wed, Fri, Sat, Sun
42.5 mg	7.5 mg on Mon, Wed, Fri; 5 mg on Tue, Thu, Sat, Sun
45 mg	7.5 mg on Mon, Tue, Thu, Sat; 5 mg on Wed, Fri, Sun
47.5 mg	7.5 mg on Mon, Tue, Wed, Fri, Sat; 5 mg on Thu, Sun
50 mg	7.5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 5 mg on Sun

High INR and bleeding: what guidelines say

Situation	Action	Source
INR above range but < 5, no bleeding	Lower the weekly dose or omit a dose (see the nomogram rows above); more frequent INR checks.	UW Medicine, BC Guidelines
INR 5.0–8.0, no bleeding	Withhold 1 or 2 doses and reduce the maintenance dose.	BNF / BSH
INR 4.5–10, no bleeding	Vitamin K is not routinely recommended — holding warfarin is usually enough.	CHEST 2012 (Grade 2B)
INR > 8 (BNF) or > 10 (CHEST), no bleeding	Stop warfarin; a clinician gives oral vitamin K and repeats the INR in 24 h; restart when INR < 5.	BNF / CHEST 2012
INR 5–8 or > 8 with minor bleeding	Stop warfarin; IV vitamin K given by a clinician; restart when INR < 5.	BNF / BSH
Major bleeding at any INR	Emergency care: stop warfarin, IV vitamin K plus prothrombin complex concentrate (4-factor PCC).	CHEST 2012, BNF

When to recheck INR after a change

Situation	Next INR
A dose was held today for significant over-anticoagulation	In 1–2 days
Dose changed today	Within 1–2 weeks
Dose changed less than 2 weeks ago (now in range)	Within 2–4 weeks
Stable, reliable patient, in range	Every 4–8 weeks (CHEST: up to 12 weeks if consistently stable)
Unstable or unreliable patient	Every 1–2 weeks
After hospital discharge	1–3 days if unstable, 3–7 days if stable

From the UW Medicine monitoring schedule; CHEST 2012 allows up to 12 weeks between tests for consistently stable patients.

INR target by indication

Indication	INR target	Source
Atrial fibrillation (non-valvular)	2.0–3.0 (aim 2.5)	CHEST
DVT or pulmonary embolism (VTE)	2.0–3.0 (aim 2.5)	CHEST
Mechanical aortic valve (bileaflet or current tilting disc), no risk factors	Aim 2.5 (2.0–3.0)	ACC/AHA 2020
Mechanical aortic valve with risk factors (AF, prior clot, LV dysfunction, hypercoagulable) or older valve	Aim 3.0 (2.5–3.5)	ACC/AHA 2020
Mechanical mitral valve	Aim 3.0 (2.5–3.5)	ACC/AHA 2020
On-X mechanical aortic valve, no risk factors, after 3 months	1.5–2.0 with aspirin	ACC/AHA 2020 (Class 2b)

DOACs (apixaban, rivaroxaban, dabigatran, edoxaban) are not used with mechanical heart valves — warfarin remains the anticoagulant for them.

Warfarin tablet colors (US and UK)

US strength	Color
1 mg	Pink
2 mg	Lavender
2.5 mg	Green
3 mg	Tan
4 mg	Blue
5 mg	Peach
6 mg	Teal
7.5 mg	Yellow
10 mg	White (dye-free)

UK strength	Color
0.5 mg	White
1 mg	Brown
3 mg	Blue
5 mg	Pink

US colors from the Coumadin label; UK colors from the emc leaflet. Always check the milligrams, not just the color.

Drugs and foods that change the INR

Drug or factor	Effect	Note
Amiodarone	Raises INR	Major; effect builds over weeks
Metronidazole, sulfamethoxazole (Bactrim), fluconazole and other azoles	Raises INR	Major; check INR within days of starting
Ciprofloxacin, levofloxacin, clarithromycin, erythromycin	Raises INR	Major
Acetaminophen (regular use)	Raises INR	Moderate; matters with daily use
Alcohol	Acute binge raises INR; chronic heavy use lowers it	Keep intake small and steady
Thyroid hormone (starting or increasing)	Raises INR	Major
Rifampin/rifamycins, carbamazepine, phenobarbital	Lowers INR	Enzyme inducers; doses may need large increases
Vitamin K (supplements, large changes in leafy greens)	Lowers INR	Keep vitamin K intake consistent, not zero
Aspirin, NSAIDs (ibuprofen, naproxen), clopidogrel	No INR change but more bleeding	Usually avoid unless prescribed together

Selected from the UW Medicine interaction table and the FDA label. Get an INR within a few days of starting or stopping any of these.

Why adjust the weekly dose, not one day

The pharmacology behind small, slow changes

Warfarin’s effective half-life is 20–60 hours (mean about 40), so any change takes roughly a week to settle. Judging a dose change after two or three days overreacts to a moving number.

The dose–INR curve is steep and non-linear, so modest dose changes can move the INR a lot. Average maintenance doses are around 4–6 mg a day but vary widely with age, genetics (CYP2C9, VKORC1), diet, liver function and other drugs.

Working in weekly totals lets small steps (2.5 mg out of 35 mg = 7%) fit what tablets can deliver. Holds and boosters fix today’s INR; the percent change fixes next week’s.

Common mistakes

What anticoagulation clinics see most

Doubling up after a missed dose. Take it the same day if you remember, otherwise skip it and never double the next dose. A low INR caused by a missed dose usually means resuming the usual weekly dose, sometimes after a one-time booster your clinic approves.
Changing the dose for a single borderline value. One INR within 0.5 of range in a stable patient usually needs only a recheck.
Juggling several tablet strengths. More strengths mean more chances for a mix-up; one strength with half tablets is simpler.
Cutting out green vegetables. Keep vitamin K intake steady instead; sudden changes move the INR.
Starting antibiotics or painkillers without telling the clinic. Many raise the INR within days.

Sources and how this calculator was checked

Every chart and example on this page is generated by the same code that runs the calculator. The dosing rows match the UW Medicine nomogram exactly; high-INR thresholds, vitamin K and recheck advice are cross-checked with CHEST 2012, the BNF and BC Guidelines.

UW Medicine Anticoagulation Services — Warfarin dosing nomogramsMaintenance nomogram for goals 2–3 and 2.5–3.5 (adapted from Crowther et al., Ann Intern Med 1997), INR recheck schedule and interaction table.
Holbrook A et al. Evidence-based management of anticoagulant therapy. CHEST 2012Single out-of-range INR rule, 12-week testing for stable patients, vitamin K thresholds and major-bleeding reversal.
Horton JD, Bushwick BM. Warfarin therapy: evolving strategies in anticoagulation. Am Fam Physician 1999Adjust the cumulative weekly dose by 10–20%; single-strength weekly schedules.
Ebell MH. Point-of-care guide to warfarin dose adjustment. Am Fam Physician 2005Worked example: 40 mg/week with INR 3.6 lowered 5–10% and rechecked in 7–14 days.
BC Guidelines — Warfarin therapy managementTop-up and 10–20% changes for low INR; omit doses and resume 10–20% lower at INR 5–9.
BNF (NICE) — Oral anticoagulants treatment summaryBSH thresholds: INR 5–8 withhold 1–2 doses; INR > 8 oral vitamin K; bleeding management.
FDA — Coumadin (warfarin sodium) prescribing informationHalf-life 20–60 hours, US tablet strengths and colors, interactions.
emc — Warfarin tablets patient information leaflet (UK)UK tablet colors: 0.5 mg white, 1 mg brown, 3 mg blue, 5 mg pink.
ACC — 2020 ACC/AHA valvular heart disease guideline: key pointsINR goals 2.5 vs 3.0 for mechanical aortic and mitral valves; On-X 1.5–2.0.

Medical disclaimer: this page is educational and does not provide medical advice. It does not cover starting doses, bridging, procedures, pregnancy, children or genotype-guided dosing. Follow the instructions of the clinician who manages your warfarin.

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