How does warfarin dose adjustment work?

When the INR drifts out of range, the total weekly dose is changed by a small percentage rather than altering a single day's tablet. Typical steps are 5 to 20 percent up or down. Working in weekly totals lets you spread the change across the week and keep daily doses practical.

What if the INR is very high?

For an INR of 4 to 9 the nomogram recommends holding one or two doses and reducing the weekly dose, and considering low-dose oral vitamin K if there is no bleeding. At an INR of 9 or above, warfarin is stopped, oral vitamin K is given, and urgent clinical review is arranged.

Should I change the dose for a single out-of-range INR?

Not always. A one-off mildly out-of-range INR with an obvious explanation, such as a missed dose, a recent antibiotic, or a change in diet, is often best rechecked rather than over-corrected. Investigate interacting drugs and adherence before adjusting maintenance.

Which target INR should I use?

Most indications, including atrial fibrillation and most venous thromboembolism, target an INR of 2.0 to 3.0. A higher target of 2.5 to 3.5 is used for some mechanical heart valves and certain other indications. Select the band your patient's indication requires.

Is this a substitute for an anticoagulation service?

No. This reproduces a common maintenance nomogram for guidance only. It assumes no active bleeding and stable adherence and diet, and it cannot account for every interaction or clinical nuance. Always follow your local anticoagulation protocol and clinician oversight.

Warfarin INR Dose Adjustment Calculator

Warfarin has a narrow therapeutic window, so keeping the INR in range means making small, structured changes to the weekly dose rather than guessing. This calculator applies a widely used maintenance nomogram to turn a current INR and weekly dose into a concrete recommended change.

How it works

The tool first places the INR into a band, then applies the percentage change that band specifies to the current total weekly dose, and finally divides by seven to suggest a daily figure.

new weekly dose = current weekly dose x (1 + percentage change / 100)
new daily dose  = new weekly dose / 7

For a target INR of 2.0 to 3.0, the bands are: below 1.5 increase 10 to 20 percent, 1.5 to 1.9 increase 5 to 10 percent, in range no change, mildly high decrease 5 to 10 percent, 4 to 9 hold doses and decrease 10 to 20 percent with possible vitamin K, and 9 or above stop and give vitamin K.

Worked example and cautions

If a patient on 35 mg per week has an INR of 1.7 with a target of 2.0 to 3.0, the nomogram suggests increasing the weekly dose by 5 to 10 percent, giving roughly 37 to 38 mg per week, or about 5.3 mg per day, with a recheck in one to two weeks. Before acting on any out-of-range INR, look for an explanation first: a new interacting drug, missed or doubled tablets, illness, or a change in dietary vitamin K can all move the INR without needing a permanent dose change. This nomogram assumes no significant bleeding and should always sit inside your local anticoagulation protocol.