How-to · Updated October 2, 2026
How do you adjust warfarin based on INR?
Direct answer
Clinics change the weekly total by about 5–20%, using a nomogram. On 5 mg daily (35 mg/week) with a 2–3 target, INR 2.5 stays at 35 mg. INR 1.7 suggests about 37.5 mg/week (+7.1%). INR 3.6 suggests holding one dose, then about 32.5 mg/week.
Nomogram for a 2–3 target
Rows through 4.9 follow the UW Medicine maintenance nomogram. INR 5 and above follows BNF/BSH high-INR guidance in this calculator. A 2.5–3.5 target shifts the lower rows up by 0.5.
| INR | Weekly change | Hold |
|---|---|---|
| < 1.5 | +10% to +20% | — |
| 1.5–1.7 | +5% to +15% | — |
| 1.8–1.9 | +5% to +10% | — |
| 2.0–3.0 | No change | — |
| 3.1–3.2 | −5% to −10% | — |
| 3.3–3.4 | −5% to −10% | Hold ½ to 1 dose |
| 3.5–3.9 | −5% to −15% | Hold 1 dose |
| 4.0–4.9 | −5% to −15% | Hold warfarin until the INR is below 3.0 |
| 5.0–8.0 | −10% to −20% | Withhold 1 or 2 doses |
| > 8.0 | −20% | Stop warfarin until the clinic advises |
5 mg every day
| INR | What the model builds |
|---|---|
| 1.7 | INR 1.7 → consider a one-time booster, then increase to about 37.5 mg per week (+7.1%). |
| 2.5 | INR 2.5 is in range (2.0–3.0) — keep 35 mg per week. |
| 3.6 | INR 3.6 → hold 1 dose, then decrease to about 32.5 mg per week (−7.1%). |
The INR 3.6 schedule with 5 mg tablets is 5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun. The INR 1.7 schedule is 7.5 mg on Mon; 5 mg on Tue, Wed, Thu, Fri, Sat, Sun.
Limits
- Educational reading of a published nomogram, not a prescription and not a reason to change, skip, or double a dose. Your clinic, pharmacist, or doctor decides.
- One INR within 0.5 of a previously stable range can stay on the same dose, with a recheck in 1–2 weeks (CHEST 2012). The model flags that when you mark the INR as stable.
- Any bleeding needs medical care now. INR above 5 needs a same-day call. INR above 8 means stop warfarin and get same-day advice. Vitamin K, when it is used, is prescribed by a clinician.
Use the calculator
The arithmetic of a percent step: how to calculate a 10% warfarin dose change. Enter an INR in the warfarin dose adjustment calculator.