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Warfarin Dose Adjustment Calculator (INR Nomogram)

Written by the Elysia Tools team · Last updated：2026-08-05

This tool is for informational purposes only and does not constitute medical, financial, or legal advice; consult a qualified professional for advice.

Adjust warfarin maintenance dose from the current INR using the standard nomogram for a target INR of 2.0–3.0. No-bleed ladder: INR<1.5 → +10–20% weekly dose; 1.5–1.9 → +5–15%; 2.0–3.0 → no change; 3.1–3.5 → −5–15%; 3.6–4.0 → −10–20%; 4.1–4.4 → hold 0–1 dose, ~−20%; 4.5–10 → hold + oral vitamin K₁ 1–2.5 mg; >10 → hold + oral vitamin K₁ 2.5–5 mg. Serious/life-threatening bleed at any INR → hold warfarin, vitamin K₁ 5–10 mg IV (slow, 20–30 min) + 4-factor PCC (FFP if unavailable). Optional current weekly dose computes the concrete new weekly and daily dose. Derived from the 9th-edition ACCP Guidelines (Holbrook et al., Chest 2012) and the UW Anticoagulation Clinic nomogram. Valid for adult maintenance therapy at steady state; not for initial induction, DOAC/heparin overlap, or perioperative bridging. Not medical advice.

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Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category
Health
Input types
number, checkbox
Output type
json
Sample coverage
4
API ready
Yes

Overview

The Warfarin Dose Adjustment Calculator uses the current INR and optional weekly warfarin dose to apply a standard nomogram for an INR target of 2.0–3.0. It returns an adjustment range, possible vitamin K recommendations, and follow-up timing for adult maintenance therapy at steady state; it is not medical advice.

When to use

  • Estimate a maintenance-dose adjustment after entering a current INR.

© 2026 Elysia Tools. All rights reserved.

Convert a recommended percentage change into an approximate weekly and daily dose by entering the current weekly dose.
  • Review the nomogram pathway for a high INR or serious bleeding, including hold, vitamin K, and PCC recommendations.

    • How it works

    1. 1Enter the current positive INR.
    2. 2Optionally enter the current total weekly warfarin dose to calculate a concrete new weekly and daily dose range.
    3. 3Select the serious or life-threatening bleeding option when applicable; this switches to the full-reversal pathway regardless of INR.
    4. 4The calculator returns the INR category, recommended action, dose-change range, vitamin K guidance, and suggested recheck interval as JSON.

    Use cases

    • Anticoagulation clinic review of an out-of-range maintenance INR.
    • Estimating weekly and daily dose ranges from a known current weekly warfarin dose.
    • Checking the appropriate nomogram pathway for elevated INR or serious bleeding before clinical action.

    Examples

    1. Subtherapeutic INR dose adjustment

    Anticoagulation clinic staff

    Background

    An adult receiving stable maintenance warfarin has an INR of 1.7 and a current weekly dose of 35 mg.

    Problem

    The INR is below the 2.0–3.0 target and the weekly dose change needs to be estimated.

    How to use

    Enter an INR of 1.7, a weekly dose of 35 mg, leave serious bleeding unchecked, and set the desired decimal places.

    {"inr":1.7,"weeklyDose":35,"seriousBleed":false,"decimalPlaces":4}

    Outcome

    The calculator identifies the subtherapeutic 1.5–1.9 category and recommends increasing the weekly dose by 5–15%, producing 36.75–40.25 mg per week or 5.25–5.75 mg per day, with an INR recheck in 7 days.

    2. High INR without bleeding

    Warfarin monitoring clinician

    Background

    An adult on maintenance warfarin has an INR of 7.0 and no serious or life-threatening bleeding.

    Problem

    The clinician needs the high-INR, no-bleed nomogram recommendation.

    How to use

    Enter an INR of 7.0, leave the weekly dose blank if a concrete dose calculation is not needed, and leave serious bleeding unchecked.

    {"inr":7,"seriousBleed":false,"decimalPlaces":4}

    Outcome

    The calculator identifies the high 4.5–10.0 no-bleed category and recommends holding warfarin, considering oral vitamin K1 1–2.5 mg, and rechecking the INR in 24 hours.

    FAQ

    What INR target does this calculator use?

    It uses the standard maintenance target range of 2.0–3.0.

    Can I calculate a new weekly warfarin dose?

    Yes. Enter the optional current weekly dose to calculate the recommended weekly and daily dose range.

    What happens if serious bleeding is selected?

    The calculator recommends holding warfarin, IV vitamin K1 5–10 mg, and 4-factor PCC, with FFP if PCC is unavailable, regardless of INR.

    Does the calculator cover high INR without bleeding?

    Yes. It provides hold and oral vitamin K1 guidance for INR ranges from 4.5 to above 10.

    Who is this calculator intended for?

    It is intended for adult maintenance therapy at steady state, not initial induction, DOAC or heparin overlap, or perioperative bridging.

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