Warfarin Dose Adjustment Calculator

Work out warfarin dose adjustment instantly with clear inputs, formula shown and shareable results.

About Warfarin Dose Adjustment Calculator

Applies the conventional 10 to 20 percent weekly dose adjustment bands used in warfarin nomograms once the INR sits outside the target range.

Formula

Weekly dose adjustment

Adjusted weekly dose = current weekly dose x (1 + percentage change), with 10-15% steps for modest deviations and dose omission above INR 5

Worked example

With the default values below, Warfarin Dose Adjustment Calculator returns Adjusted weekly dose of 29.8. Change any input above and every figure here is recalculated in your browser.

Inputs used

Current weekly doseaccepts 3–120 mg: 35 mg
Current INRaccepts 0.8–10: 4.2
Target rangeone of 2.0 to 3.0, 2.5 to 3.5: 2.0 to 3.0

Results

Adjusted weekly dose: 29.8 mg
Change applied: -15%
Suggested action: Well above range — omit one dose then reduce the weekly total
Average daily dose: 4.25 mg

Step by step

1Values used
2Weekly dose adjustment
3Adjusted weekly dose= 29.8 mg
4Change applied= -15
5Suggested action= Well above range — omit one dose then reduce the weekly total
6Average daily dose= 4.25 mg

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

Why adjust the weekly rather than daily dose?

Warfarin has a long half-life, so spreading a small change across the week avoids large swings.

How soon should the INR be rechecked?

Usually within 4 to 7 days of a dose change, sooner if the INR was far outside range.