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Educational warfarin (Coumadin) dose adjustment from measured INR and goal range. Applies percent change to total weekly milligrams—tablet-agnostic. Flags when INR ≥5 requires clinician management, not home math. Pair with CHA₂DS₂-VASc. Not a prescription.
Last updated: June 5, 2026
Follow your anticoagulation clinic or prescriber. High INR, bleeding, procedures, and pregnancy require individualized protocols beyond this page.
How do you track dose?
INR 3.1–3.4
INR modestly above target
Some clinics reduce total weekly dose slightly (~5–10%) or omit one dose when INR is just above goal. Exact steps vary by center and bleeding risk.
Equivalent weekly total: 35.0 mg/week
Suggested change to weekly total: -7.5%
Rounded suggested weekly total: 32.5 mg/week
≈ average daily if split evenly: 4.64 mg/day
Recheck INR in 2–7 days after adjustment.
Not medical advice
Warfarin dosing must follow your anticoagulation clinic or prescriber. Tablet strengths vary (1, 2, 2.5, 3, 4, 5, 6, 7.5, 10 mg). This tool does not replace protocols for bridging, procedures, pregnancy, or liver failure.
In range — INR 2.5, 35 mg/week
0%
INR 2.0–3.0
Below target — INR 1.7, 42 mg/week
+7.5% → 45 mg/wk
INR 1.5–1.9 (target 2–3)
Above target — INR 3.2, 35 mg/week
-7.5% → 32.5 mg/wk
INR 3.1–3.4
Tight target low — INR 2.2, 40 mg, 2.5–3.5
+7.5% → 43 mg/wk
INR 2.0–2.4
High INR — 5.2, 35 mg/week (no home % math)
Clinician-directed
INR 5.0–8.9
Simplified teaching bands—institutional anticoagulation protocols are the standard of care.
| INR | Weekly % change | Typical action |
|---|---|---|
| < 1.5 | +15% | Subtherapeutic — increase weekly total ~10–20% |
| 1.5 – 1.9 | +7.5% | Slightly below 2.0 — modest increase |
| 2.0 – 3.0 | 0% | Therapeutic — maintain dose |
| 3.1 – 3.4 | −7.5% | Modestly above — small reduction or hold 1 dose |
| 3.5 – 3.9 | −10% | Hold dose(s) + reduce ~10–15% |
| 4.0 – 4.9 | −15% | Hold + larger reduction; clinician contact |
| 5.0 – 8.9 | Clinician only | No home % math — hold warfarin |
| > 9 | Urgent care | Emergency evaluation if bleeding |
| INR | Weekly % change | Typical action |
|---|---|---|
| < 2.0 | +15% | Below tighter range — larger upward adjustment |
| 2.0 – 2.4 | +7.5% | Approaching lower bound 2.5 |
| 2.5 – 3.5 | 0% | In therapeutic window — maintain |
| 3.6 – 4.0 | −10% | Above 3.5 — hold + reduce |
| 4.1 – 4.9 | −15% | Elevated — hold + clinical guidance |
| ≥ 5.0 | Clinician only | Physician-directed management |
| Indication | Target | Note |
|---|---|---|
| Atrial fibrillation (non-valvular) | 2.0 – 3.0 | Most common outpatient target |
| DVT / PE treatment | 2.0 – 3.0 | Often 3 months then reassess |
| Mechanical mitral valve | 2.5 – 3.5 (or higher) | Valve-specific protocols vary |
| Mechanical aortic valve (modern) | 2.0 – 3.0 often | Lower targets with bileaflet valves |
| Recurrent VTE on warfarin | 2.5 – 3.5 sometimes | Individualized by hematology |
| Aspect | Warfarin | DOACs |
|---|---|---|
| Monitoring | INR blood test (target 2–3 or 2.5–3.5) | No routine INR; renal/hepatic dosing |
| Dose adjustment | Weekly mg total titrated from INR | Fixed/weight-based — rarely INR-guided |
| Reversal | Vitamin K, PCC, FFP in bleeding | Specific antidotes (idarucizumab, andexanet) per agent |
| Diet | Consistent vitamin K intake matters | Minimal food interaction |
| Agent | INR effect | Action |
|---|---|---|
| Amiodarone | Raises INR — often requires 30–50% dose reduction | Report to clinic immediately |
| Antibiotics (macrolides, fluoroquinolones) | Often raises INR via CYP inhibition / gut flora | Earlier INR check when starting course |
| Rifampin | Lowers INR via enzyme induction | May need substantial dose increase |
| Acetaminophen (chronic high dose) | Modest INR elevation | Report regular use >2 g/day |
| Herbal supplements (St. John's wort) | Lowers INR | Avoid without clinician approval |
| Strength | Typical color | Note |
|---|---|---|
| 1 mg | Pink (varies by manufacturer) | Fine-tuning increments |
| 2 mg | Lavender | Common in alternating schedules |
| 2.5 mg | Green | Frequent starter strength |
| 5 mg | Peach | Typical maintenance tablet |
| 10 mg | White | Higher weekly totals |
| INR situation | Teaching action | Note |
|---|---|---|
| 4.5 – 10, no bleeding | Hold warfarin; repeat INR — oral vit K 1–2.5 mg sometimes | Clinician decision only |
| > 10, no bleeding | Hold warfarin + oral vit K 2.5–5 mg often discussed | Not self-administer from this page |
| Any INR + serious bleeding | Emergency care + IV vitamin K / PCC | Do not wait for calculator |
Some clinics reduce total weekly dose slightly (~5–10%) or omit one dose when INR is just above goal. Exact steps vary by center and bleeding risk.
Educational disclaimer: This calculator applies simplified INR-band percent changes for learning and visit-prep. It is not a prescription, vitamin K protocol, bridging plan, or procedure hold guideline. Warfarin dosing must follow your anticoagulation clinic. Seek emergency care for bleeding, head injury, or INR >9.
Share with others on warfarin—remind them to follow their anticoagulation clinic.
Suggested hashtags: #Warfarin #Anticoagulation #INR #Coumadin #Calculator