How-to · Updated October 2, 2026
How do you calculate a 10% warfarin dose change?
Direct answer
Multiply the weekly total by 0.10. 35 mg minus 10% is 31.5 mg. With 5 mg tablets the nearest even week is 32.5 mg (5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun). Going from 44 mg to 47 mg is +6.8%.
35 mg a week, 5 mg tablets
| Change | Exact weekly total | Nearest tablet week |
|---|---|---|
| −10% | 31.5 mg | 32.5 mg (−7.1%) — 5 mg on Mon, Tue, Wed, Thu, Fri, Sat; 2.5 mg on Sun |
| +10% | 38.5 mg | 37.5 mg (+7.1%) — 7.5 mg on Mon; 5 mg on Tue, Wed, Thu, Fri, Sat, Sun |
| −20% | 28 mg | 27.5 mg (−21.4%) — 5 mg on Mon, Tue, Thu, Sat; 2.5 mg on Wed, Fri, Sun |
−10% of 35 mg = −3.5 mg → 31.5 mg per week (4.5 mg per day on average).
From 44 mg to 47 mg
- Current: 44 mg per week.
- Change = (47 mg − 44 mg) ÷ 44 mg × 100 = +6.8%.
- Schedule with 1 mg tablets (halves allowed): 7 mg on Mon, Wed, Fri; 6.5 mg on Tue, Thu, Sat, Sun = 47 mg/week (+6.8% actual).
Limits
- This is the arithmetic clinics use. It is not a prescription. Do not start a new weekly total unless your anticoagulation clinic told you to.
- Warfarin’s effect takes several days. A new weekly total is usually rechecked in 1–2 weeks, not the next morning.
- Typical maintenance steps stay inside about 5–20%. A larger jump belongs with the prescriber, along with any bleeding or an INR above 5.
Use the calculator
Matching a percent to an INR row: how to adjust warfarin based on INR. Run a weekly total in the warfarin dose adjustment calculator.