Calculate warfarin (Coumadin) dose adjustments from current INR, target range, bleeding status, and weekly dose, plus tablet counts.
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Coumadin Adjustment Formula
The Coumadin Adjustment Calculator uses the current INR, target INR range, bleeding status, and current weekly warfarin dose to estimate a maintenance dose adjustment. It also converts a weekly dose into daily tablet counts when you use the tablet count tab.
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)
Average dose per dosing day
Average\ Daily\ Dose = Weekly\ Dose / Dosing\ Days
Previous dose mode weekly total
Weekly\ Dose = Mon + Tue + Wed + Thu + Fri + Sat + Sun
Tablet count mode
Tablets\ Per\ Dosing\ Day = (Weekly\ Dose / Dosing\ Days) / Tablet\ Strength
Rounded\ Weekly\ Dose = Rounded\ Tablets\ Per\ Day * Tablet\ Strength * Dosing\ Days
- Current Weekly Dose: the total warfarin dose currently taken per week, in mg/week.
- Adjustment Percent: the selected percentage increase or decrease based on the INR band and target range.
- Dosing Days: the number of days per week warfarin is taken.
- Average Daily Dose: the weekly dose divided across dosing days.
- Tablet Strength: the strength of one warfarin tablet, in mg/tablet.
- Rounded Tablets Per Day: the tablet count rounded to the selected increment, such as nearest half tablet.
Adjustment tab: You enter the current INR and current weekly dose. The calculator selects an INR-based recommendation, then applies the dose increase or decrease formula when a numeric change is appropriate.
Previous Dose tab: You enter each daily dose from the prior schedule. The calculator adds the seven daily doses to get the weekly dose, then applies the same adjustment logic.
Tablet Count tab: You enter a desired weekly dose and tablet strength. The calculator converts mg/week into tablets per dosing day and shows the effect of rounding.
INR Bands and Typical Maintenance Actions
| Target INR | Current INR band | Typical calculator action | Suggested recheck |
|---|---|---|---|
| 2.0 to 3.0 | Below 1.8 | Increase maintenance dose, often 5% to 20% depending on INR | 3 to 7 days |
| 2.0 to 3.0 | 2.0 to 3.0 | Usually no dose change | Up to 4 weeks |
| 2.0 to 3.0 | Above 3.0 but below 5.0 | Decrease dose and/or omit a dose, depending on INR band | Daily to 7 days, depending on elevation |
| 2.5 to 3.5 | Below 2.3 | Increase maintenance dose, often 5% to 20% depending on INR | 3 to 7 days |
| 2.5 to 3.5 | 2.5 to 3.5 | Usually no dose change | Up to 4 weeks |
| Either target | Serious bleeding, life-threatening bleeding, or very high INR | Do not calculate a routine outpatient maintenance change. Urgent clinical management is needed. | Same day or emergency care |
Common Warfarin Tablet Strengths
| 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: Increase weekly dose for low INR
You have a current INR of 1.6, a target INR of 2.0 to 3.0, and a current weekly warfarin dose of 35 mg/week. The calculator may recommend increasing the maintenance dose by 5% to 15%.
Low\ End = 35 * (1 + 5/100) = 36.75\ mg/week
High\ End = 35 * (1 + 15/100) = 40.25\ mg/week
The adjusted weekly dose range is about 36.75 to 40.25 mg/week before converting to a practical tablet schedule.
Example 2: Convert weekly dose to tablets
You want a weekly dose of 35 mg/week using 5 mg tablets, taken 7 days per week.
Daily\ Dose = 35 / 7 = 5\ mg/day
Tablets\ Per\ Day = 5 / 5 = 1\ tablet/day
The tablet schedule is 1 tablet per day, giving 35 mg/week.
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.
What does “two previous INRs in range” change?
If the last two INRs were therapeutic, a small INR change just outside the target range may not require an immediate dose change. The calculator uses that input to allow a no-change option for slight INR deviations when the recent trend has been stable.
