Using an ovulation predictor test is, in many ways, an exercise in guesswork. You don’t want to start using the ovulation test any sooner than you need to, otherwise you will be wasting your test materials. On the other hand, if you wait too many days after your period is over to use an ovulation test, you might miss that all-important LH surge that the ovulation test is designed to measure. For this reason, you will need to do some calculating about exactly how many days into your cycle you should use an ovulation test.

In all actuality, you are not going to measure the start of using your ovulation tests from the end of your period, but rather from the beginning of your period, which is the start of your monthly cycle. If you have an average 28-day cycle, for example, you should use an ovulation test beginning on day 11 after the start of your cycle. If you have a longer cycle, you will increase the starting day by the number of days longer than 28 your cycle is. For example, if your cycle is generally 32 days long, you will want to start using an ovulation test at around day 15 of your cycle. On the other hand, if you have a shorter cycle, you will want to test earlier. If you have a 24-day cycle, then, you would test on day 7 after the start of your period. In some cases, your period might not even be over by the time you should use your ovulation test.

If your cycle tends to vary, it is a little more difficult. You should use the shortest cycle that you have had in the last six months, and start testing on the appropriate day for that length. If your cycle varies greatly, it is possible that you would have to use 10 or more ovulation tests before you are able to detect your LH surge. While this is not especially common, it certainly is a possibility.