Calculator Inputs
Use the form below for warfarin maintenance review. Results appear above this form after submission.
Example Data Table
| Week | Target Range | INR | Weekly Dose (mg) | Suggested Action | Next Check |
|---|---|---|---|---|---|
| Week 1 | 2.0 - 3.0 | 1.6 | 35 | Increase 5% to 15% and consider booster | 2 weeks |
| Week 2 | 2.0 - 3.0 | 2.4 | 37 | Stay on current dose | Up to 8 weeks |
| Week 3 | 2.0 - 3.0 | 3.3 | 37 | Reduce 5% to 10%, consider partial hold | 2 weeks |
| Week 4 | 2.5 - 3.5 | 4.8 | 42 | Hold 1 to 2 doses and reduce 5% to 15% | 1 week |
| Week 5 | 2.5 - 3.5 | 6.7 | 40 | Hold doses, lower weekly dose, escalate review | Within 5 days |
Formula Used
Weekly adjusted dose = Current weekly dose × (1 ± adjustment percentage)
Average daily dose = Weekly adjusted dose ÷ 7
Booster estimate = Current daily maintenance dose × 1.5 to 2.0, when a one-time increase is suggested.
The calculator applies maintenance nomogram percentage changes to the total weekly dose. Small out-of-range values usually need modest 5% to 10% changes, while larger deviations may need 10% to 20% changes, temporary dose holds, and earlier rechecks.
How to Use This Calculator
- Select the indication or target range that best matches the patient.
- Enter the current INR and the present total weekly warfarin dose.
- Add the previous INR to review the direction of change.
- State whether recent INRs were stable and whether a temporary explanation exists.
- Choose the bleeding status honestly. Active bleeding should trigger urgent clinician review.
- Press Calculate Adjustment to show the recommendation above the form.
- Use the CSV or PDF buttons to save the summary for documentation.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates maintenance warfarin dose changes from an out-of-range INR, current weekly dose, target range, and follow-up timing. It is designed for structured review, not autonomous prescribing.
2. Is this tool appropriate for new warfarin starts?
No. It is meant for maintenance therapy after the initial dosing phase. Initiation schedules depend on baseline risk, sensitivity, interacting medicines, and closer monitoring patterns.
3. What if the patient has bleeding?
Do not rely on routine maintenance percentages. Bleeding requires urgent clinician-directed evaluation, possible dose holding, and sometimes reversal planning, depending on severity and the INR result.
4. Why does the tool ask about recent stable INRs?
Small INR drifts near range often do not need a maintenance change when the last two results were stable. The calculator reflects that more conservative approach.
5. Why is weekly dose used instead of a single daily dose?
Warfarin plans are commonly adjusted as a percentage of the total weekly dose. That makes it easier to create uneven daily schedules while preserving the intended total exposure.
6. Can I use a custom target range?
Yes, but the custom option is advisory only. Automated percentage adjustments in this calculator are intentionally limited to the common 2.0–3.0 and 2.5–3.5 maintenance targets.
7. What do the CSV and PDF buttons save?
They save the current result summary, including the target range, INR, weekly dose, proposed change, one-time action, next check interval, and notes for documentation.
8. Should a temporary cause change the plan?
Often yes. Missed doses, extra doses, diet shifts, alcohol changes, illness, and interacting drugs may explain the result. Once resolved, returning to the prior maintenance dose may be reasonable.