Enter INR Data
Use one reading per line in YYYY-MM-DD, INR format.
Example Data Table
This sample shows how INR readings can be prepared before pasting into the calculator.
| Date | INR | Interpretation | Expected Action |
|---|---|---|---|
| 2026-01-02 | 2.1 | Within target | Continue usual monitoring plan. |
| 2026-01-09 | 2.4 | Within target | Maintain current dose if clinically appropriate. |
| 2026-01-16 | 2.7 | Within target | Stable control supports current follow-up interval. |
| 2026-01-30 | 3.1 | Above target | Review dose, diet, illness, and interactions. |
| 2026-02-10 | 2.8 | Within target | Recheck after adjustment or routine interval. |
Formula Used
Rosendaal TTR estimates the percentage of days spent within the target INR range by linearly interpolating INR values between two test dates.
Interpolated daily INR: INRday = INR1 + ((day offset ÷ interval days) × (INR2 − INR1)).
Rosendaal TTR (%): (days within target ÷ eligible interpolated days) × 100.
Point-in-range percentage: (number of readings within target ÷ total readings) × 100.
Average INR: sum of recorded INR values ÷ total readings.
Variation spread: highest INR − lowest INR. This helps flag unstable anticoagulation, though it does not replace clinical judgment.
How to Use This Calculator
- Enter the therapeutic INR range used for the patient.
- Paste each INR result on a new line using YYYY-MM-DD, value.
- Set the maximum interpolation gap if long monitoring gaps should be excluded.
- Optionally ignore early initiation days when therapy was not yet stable.
- Click Calculate TTR to view Rosendaal TTR, point-in-range, and interval details.
- Download CSV for records or PDF for a printable review sheet.
Frequently Asked Questions
1. What does TTR mean here?
Here, TTR means time in therapeutic range for warfarin monitoring. It estimates how much time a patient’s INR stayed inside the planned target range.
2. Why use the Rosendaal method?
It estimates daily INR values between blood tests instead of counting only measured points. That gives a more time-sensitive view of anticoagulation control.
3. What is the point-in-range percentage?
It is the share of actual INR readings that fall inside the target range. It is simpler than Rosendaal TTR but less detailed.
4. Can I exclude long gaps between tests?
Yes. The maximum gap field stops interpolation across long intervals, which may reduce misleading estimates when monitoring was interrupted.
5. Should initiation days always be counted?
Not always. Some clinics exclude early days because warfarin dosing is still being stabilized. This calculator lets you ignore a selected number of starting days.
6. What TTR level is usually considered good?
Many reports consider 65% or higher a useful benchmark, though the appropriate goal can vary by patient, clinic, and indication.
7. Does this calculator replace medical advice?
No. It is a record review and estimation tool. Dose changes and safety decisions should always be made by a qualified clinician.
8. Can this be used for medicines other than warfarin?
It is designed for INR-based therapeutic range tracking. It should only be used where that approach matches the clinical monitoring method.