Enter the INR value from your blood test report
Optional — for context in your result summary
Optional — helps assess how current your result is
INR Status
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Sources & Methodology
INR ranges based on guidelines from the American College of Chest Physicians (ACCP) and ACC/AHA. Updated March 2026.
American College of Chest Physicians (ACCP)
CHEST Antithrombotic Therapy guidelines — the primary reference for therapeutic INR ranges
MedlinePlus — PT/INR Test
NIH reference for INR normal values, what the test measures, and clinical interpretation
ACC/AHA Clinical Guidelines
Anticoagulation management guidelines for atrial fibrillation and mechanical heart valves
Methodology: INR status is determined by comparing the entered value against the standard therapeutic range for the selected indication. Ranges follow ACCP 10th Edition antithrombotic guidelines. Status is classified as: Sub-therapeutic (<lower bound), Therapeutic (within range), Supra-therapeutic (>upper bound), or Critically High (>5.0).
⏱ Last reviewed: March 2026
What Is INR and What Does Your Result Mean?
INR stands for International Normalized Ratio — a standardized measurement of how long it takes your blood to clot. It's the most important test for patients on warfarin (Coumadin) anticoagulation therapy.
How INR Is Calculated
INR is derived from the Prothrombin Time (PT) test. Because different labs use different reagents, INR was developed to standardize results across all laboratories worldwide.
INR = (Patient PT ÷ Mean Normal PT) ^ ISI
ISI = International Sensitivity Index of the reagent used by the lab.
A normal INR of 1.0 means clotting time equals the average healthy person.
INR of 2.0 = blood takes twice as long to clot as normal.
A normal INR of 1.0 means clotting time equals the average healthy person.
INR of 2.0 = blood takes twice as long to clot as normal.
INR Therapeutic Ranges by Condition
| Condition | Target INR Range | Risk if Below | Risk if Above |
|---|---|---|---|
| Atrial Fibrillation (AFib) | 2.0 – 3.0 | Stroke | Bleeding |
| Deep Vein Thrombosis (DVT) | 2.0 – 3.0 | Clot extension/recurrence | Hemorrhage |
| Pulmonary Embolism (PE) | 2.0 – 3.0 | PE recurrence | Bleeding |
| Mechanical Heart Valve | 2.5 – 3.5 | Valve thrombosis/stroke | Bleeding |
| Bioprosthetic Valve | 2.0 – 3.0 | Thromboembolism | Bleeding |
| Normal (no warfarin) | 0.8 – 1.2 | N/A | Possible disorder |
💡 Time in Therapeutic Range (TTR): Studies show that patients with TTR above 70% (spending 70%+ of time within their INR target) have significantly lower rates of stroke AND bleeding. This is why consistent INR monitoring and stable warfarin dosing matters so much.
Frequently Asked Questions
For people not on anticoagulants, a normal INR is 0.8–1.2. This means blood clots at a normal rate. If your INR is elevated above 1.2 and you're NOT on warfarin, it may indicate liver disease, vitamin K deficiency, or a clotting factor disorder — speak with your doctor.
The standard therapeutic range for most warfarin patients (AFib, DVT, PE) is 2.0–3.0. For mechanical heart valve patients, the target is 2.5–3.5. An INR below target means inadequate anticoagulation (clot risk). An INR above target means excess anticoagulation (bleeding risk). Your provider sets your specific target.
An INR of 3.0–4.0 represents mild over-anticoagulation — your provider may hold a dose or reduce your weekly dose. An INR of 4.0–5.0 is moderate — warfarin is usually held and possibly vitamin K given. An INR above 5.0 is dangerously high — seek immediate medical care. Warning signs include unusual bruising, blood in urine/stool, or severe headache (possible brain bleed).
Vitamin K-rich foods (kale, spinach, broccoli, Brussels sprouts) lower INR by counteracting warfarin. Grapefruit, cranberry juice, and many herbal supplements can raise INR unpredictably. The key is consistency — don't eliminate vitamin K foods, just eat similar amounts each week. Sudden dietary changes cause INR fluctuations.
When starting warfarin: every 1–3 days. Once approaching target: weekly. Once stable: every 2–4 weeks. Most stable patients check every 4 weeks. Certain situations require more frequent testing: illness, antibiotic use, significant dietary changes, or adding/removing other medications. Home INR testing devices (Coaguchek) are available for some patients.
No. This calculator is for educational purposes only — it helps you understand what your INR result means. Warfarin dosing adjustments must be made by your anticoagulation clinic, pharmacist, or physician. Warfarin has a narrow therapeutic index and many drug/food interactions. Self-adjusting your dose can be dangerous.
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