There is halachic debate regarding veset observance when a woman consistently starts bleeding only after the onah beinonit has passed. We follow the view that a woman with at least three consecutive intervals of 32 days or more is exempt from observing onah beinonit and yom hachodesh, and observes only the interval. (If she later experiences a shorter cycle, she returns to observing all of the onot.)

If we understand you correctly, at this point you need only observe the interval. You calculate this veset as usual, based on the interval between your last two periods, even though you anticipate that it will lengthen. (If you notice a perfectly precise pattern, where the interval increases by a fixed number of days each cycle (e.g., 33, 37, 41, 45...), please write back to us for further guidance.)

If and when you no longer become niddah while taking these active pills, you may be able to switch to observing a veset based on the interval between cessation of active pills and becoming niddah. Learn more here.

Please do note that it is very common for women to experience breakthrough bleeding when extending the cycle with contraceptive pills, even after they have been doing so for some time. Please be in touch if and when other questions arise. You may also find it helpful to review the laws of staining, which can be found on our pages on Stains and Toilet Paper.

B'hatzlacha!