Time in Therapeutic Range (Rosendaal)
Warfarin time in therapeutic range (Rosendaal 1993): linear INR interpolation between dated values; TTR = days-in-range / total-days.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Dated INR values
- 2026-01-01 1.5 2026-01-11 2.5 2026-01-21 2.8
- Target INR low
- 2.0
- Target INR high
- 3.0
Result: TTR 80% — 16 of 20 days in range 2.0–3.0.
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Good control
- Commonly defined as TTR ≥ 65%.
What you enter
- Dated INR values (one per line, YYYY-MM-DD INR)
- Target INR low (defaults to 2.0, which the reading names)
- Target INR high (defaults to 3.0, which the reading names)
How this is calculated
- Method
- An INR is linearly interpolated across the days between measurements; TTR = days-in-range / total-days.
Rosendaal FR, Cannegieter SC, van der Meer FJM, Briët E. A method to determine the optimal intensity of oral anticoagulant therapy. Thromb Haemost. 1993;69(3):236-239. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.