You will get a PT/INR test before you begin taking warfarin, and then again after about 3 doses of warfarin. Doctor will then adjust your warfarin dose to get your PT/INR to the right level. For most people that means an INR between 2 and 3. You might need PT/INR tests every few days for a while, to make sure you're taking the right dose of warfarin. Once your test result stays the same for at least 1 to 2 weeks, you can probably get tests just once a month. You might have a PT/INR test more often if something changes, such as if you get sick, start a new medicine that affects your PT/INR, or have any bleeding.