Warfarin Dose Adjustment Calculator
Estimate warfarin dose adjustments based on current INR and target therapeutic range. Therapeutic INR is 2.0-3.0 for most indications. Dose changes should be 5-20% and rechecked in 3-7 days.
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Adjust warfarin doses based on INR results.
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Why: Adjust warfarin doses based on INR results.
How: Enter your values in the calculator fields below, keep units consistent, then run the calculation to see results and any step-by-step work shown on this page.
Run the calculator when you are ready.
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Important: Warfarin dosing requires clinical judgment. This calculator provides guidelines only. Always verify with institutional protocols.
For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
Warfarin (Coumadin) is a vitamin K antagonist anticoagulant. Therapeutic INR is 2.0-3.0 for most indications. Dose changes should be 5-20% and rechecked in 3-7 days. Warfarin has 36-42 hour half-life; full effect in 5-7 days.
Sources: ACCP, AHA, FDA, Lexicomp.
Key Takeaways
- • Therapeutic INR 2.0-3.0 for AFib, DVT/PE; 2.5-3.5 for mechanical mitral valve
- • Dose changes 5-20%; don't adjust too frequently (3-5 day delay)
- • Keep vitamin K intake consistent; don't avoid greens
- • INR ≥5: Hold 1-2 doses; INR ≥9: Hold + Vitamin K
Did You Know?
How Does This Calculator Work?
INR Below Target
Increase weekly dose 5-15%. Significantly low may need 10-15% increase. Recheck in 1-2 weeks.
INR Above Target
Decrease 5-20% or hold doses. INR 5-9: Hold 1-2 doses. INR 9+: Hold + Vitamin K 2.5-5 mg PO.
Weekly Schedule
Calculator creates daily dosing schedule to achieve weekly target using available tablet strengths.
Expert Tips
INR Target Ranges by Indication
| Indication | Target INR |
|---|---|
| Atrial Fibrillation | 2 - 3 |
| DVT/PE Treatment | 2 - 3 |
| Mechanical Aortic Valve | 2 - 3 |
| Mechanical Mitral Valve | 2.5 - 3.5 |
| Antiphospholipid Syndrome | 2 - 3 |
Frequently Asked Questions
What is the therapeutic INR range for warfarin?
Therapeutic INR is 2.0-3.0 for most indications (AFib, DVT/PE). Mechanical mitral valve requires 2.5-3.5. Dose changes should be 5-20% and rechecked in 3-7 days.
How is warfarin dose adjusted when INR is low?
When INR is below target, increase weekly dose by 5-15% depending on how far below. Significantly subtherapeutic (>0.5 below) may need 10-15% increase. Recheck INR in 1-2 weeks.
What should I do if INR is elevated?
INR 3.0-4.5: Reduce dose or hold 1-2 doses. INR 5.0-9.0: Hold 1-2 doses, consider vitamin K 1-2.5 mg PO if bleeding risk. INR >9: Hold warfarin, give vitamin K 2.5-5 mg PO.
How long does warfarin take to reach full effect?
Warfarin has a 36-42 hour half-life. Peak effect is 2-3 days; full effect 5-7 days. INR changes are seen 2-3 days after dose change. Don't adjust too frequently.
Can I eat green vegetables on warfarin?
Yes! Don't avoid vitamin K foods—keep intake consistent from week to week. Sudden diet changes affect INR. A dietitian can help plan a heart-healthy diet with consistent vitamin K.
When should I switch from warfarin to a DOAC?
DOACs are preferred for most AFib and VTE due to convenience and lower ICH risk. Warfarin remains preferred for mechanical valves, antiphospholipid syndrome, and severe renal disease (CrCl <15-25).
Key Statistics
Official Data Sources
⚠️ Disclaimer: This calculator is for educational purposes only. It is not a substitute for professional medical advice. Warfarin dosing requires clinical judgment. Always verify with institutional protocols and consider individual patient factors.
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