CoaglyFree INR tools
The same calculations Coagly runs on your phone, free in your browser. Everything happens on your own device — your readings are saved in this browser only, and nothing is ever uploaded to us or anyone else.
Time in therapeutic range calculator
Enter your target range and your past INR results. This applies the Rosendaal linear interpolation method — the standard anticoagulation clinics use — to work out what share of your days, not your tests, were spent in range.
1. Your target range
Not sure what yours is? It is on your anticoagulation record — or see the INR range chart.
2. Your INR results
| Date | INR | Status |
|---|
How this is calculated
Between each pair of consecutive readings, an INR is estimated for every day by drawing a straight line between the two values. Each of those days is checked against your target range, and in-range days are divided by total days assessed. Intervals longer than 56 days are excluded, because nothing is genuinely known about untested stretches that long — if any of yours are dropped, you are told rather than handed a flattering number.
Above 70% is generally regarded as good control, 65% is the common quality benchmark, and below 60% is treated as poor control. Full guide to TTR →
PT to INR converter
If your lab reported a prothrombin time in seconds rather than an INR, convert it here. You need two values from your own report: the lab's normal mean PT and the reagent's ISI.
The normal mean and ISI are properties of the lab and reagent, and are usually printed on your report. The values above are placeholders to demonstrate the formula — replace both with your own.
INR = ( TP ÷ normal mean PT ) ISI
A PT ratio is only the same as an INR when the ISI is exactly 1.0. For any other reagent the ratio must be raised to the power of the ISI, and the difference is often clinically meaningful. Full guide to PT and INR →
Next INR test planner
Work out when your next blood draw is due, and download a calendar file with a reminder already attached the day before.
Typical intervals: every 2–4 days when starting warfarin, weekly to fortnightly while stabilising, and every 4 weeks once stable. Your clinic sets yours. How often should you test? →