Warfarin Dosing Calculator

Your details

Initiation mode estimates a first maintenance dose. Adjustment mode adjusts an existing weekly dose based on the latest INR.
Patient age in whole years. Adults only (18 and over).
years
Used to calculate body surface area via the DuBois formula.
kg
Used to calculate body surface area via the DuBois formula.
cm
The Gage algorithm found African-American patients require a modestly higher dose on average. This reflects population pharmacokinetics, not an absolute rule.
Your clinical target INR. Most AF, DVT, and PE patients aim for 2-3 (midpoint 2.5). Mechanical heart valves usually target 2.5-3.5.
Amiodarone strongly inhibits CYP2C9 and substantially reduces warfarin clearance, requiring a lower starting dose.
Cigarette smoking induces CYP1A2 and marginally affects warfarin metabolism; smokers tend to need a slightly higher dose.
DVT/PE as the indication was associated with a slightly higher required dose in the derivation cohort.
Estimated daily doseModerate dose range
4.63mg/day

Gage 2004 algorithm predicted maintenance dose per day

Estimated weekly dose32.4mg/week
Body surface area1.864m²
4.63 mg/day
Low<3Moderate3-7High7+

Estimated warfarin starting dose: 4.63 mg/day

  • The Gage algorithm predicts a starting maintenance dose of about 4.63 mg/day (32.4 mg/week).
  • This is an estimated starting point only. After initiation, dose is titrated based on serial INR measurements using a maintenance nomogram.
  • Body surface area: 1.864 m² (DuBois formula). Larger BSA = higher predicted dose.

Next stepThis tool provides a clinical estimate, not a prescription. The starting dose must be confirmed and adjusted by a licensed clinician, with INR checks typically on days 3, 5, and 7 after initiation.

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