Calculate a new weekly warfarin (Coumadin) dose from a clinician-directed percentage change, or the percent change between two doses, with an INR check.

Use only for a clinician-directed change. Do not change, skip or double warfarin from this arithmetic alone. Seek urgent medical help for severe or uncontrolled bleeding.

Total across the current seven-day schedule.

Enter the percentage supplied by the managing clinician.

INR comparison (optional)

Coumadin Adjustment Formula

This calculator applies a percentage change supplied by your prescribing clinician or calculates the percentage difference between two weekly doses. Optional INR context compares your result with the prescribed range you enter; it does not select a dose adjustment, tablet schedule or next test date.

Maintenance dose increase

New Weekly Dose = Current Weekly Dose × (1 + Adjustment Percent / 100)

Maintenance dose decrease

New Weekly Dose = Current Weekly Dose × (1 - Adjustment Percent / 100)

Seven-day arithmetic average

Weekly total ÷ 7 gives an arithmetic average, not a daily prescription. Actual daily doses may vary according to the prescribed schedule.

Percentage between weekly doses

Percentage change = (prescribed weekly total − current weekly total) ÷ current weekly total × 100. A negative percentage means a decrease. The current total must be greater than zero.

INR Context and Clinical Decisions

Your anticoagulation clinician chooses the target INR, any dose change and the next INR test after reviewing your INR trend, bleeding, missed doses, medicines, diet and illness. Follow your prescribed plan rather than selecting an adjustment from a general INR table. Severe or uncontrolled bleeding needs urgent medical help.

Common Warfarin Tablet Strengths

Verify the medicine, strength and splitting instructions on your own packaging with your pharmacist; do not identify a tablet by color alone.

Tablet strength Common tablet color Example half-tablet dose
1 mg Pink 0.5 mg
2 mg Lavender 1 mg
2.5 mg Green 1.25 mg
5 mg Peach 2.5 mg
7.5 mg Yellow 3.75 mg
10 mg White 5 mg

Coumadin Adjustment Examples

Example 1: Hypothetical clinician-directed increase

If the managing clinician instructs a 10% increase from 35 mg/week, the arithmetic is 35 × 1.10 = 38.5 mg/week. The clinician must provide the actual tablet schedule.

Example 2: Percentage difference

Comparing a current 35 mg/week with a prescribed 31.5 mg/week gives (31.5 − 35) ÷ 35 × 100 = −10%. This comparison does not decide whether the change is appropriate.

Coumadin Adjustment FAQ

Can I change my Coumadin dose based only on this result?

No. Warfarin dose changes should be reviewed against clinical factors such as bleeding, missed doses, diet changes, alcohol intake, illness, new medications, antibiotics, amiodarone, antifungals, and liver function. If there is serious bleeding, life-threatening bleeding, or a very high INR, urgent medical care is needed instead of a routine maintenance adjustment.

Why does the calculator use weekly dose instead of only daily dose?

Warfarin is often adjusted by changing the total weekly dose because small percentage changes are easier to manage over a full week. For example, changing from 35 mg/week to about 38.5 mg/week may be handled by adding one or two higher-dose days rather than changing every day equally.

Does INR context recommend a dose?

No. It only compares the entered INR against the prescribed target range you supply. It does not use that comparison to change the dose or choose a monitoring interval.

Source: FDA-approved warfarin labeling, revised June 2026.