Period Calculator

Your typical cycle length is enough to project three things at once: when your next period should arrive, when you are most fertile, and which day ovulation likely falls on. Those dates support family planning, help you get ahead of period symptoms, and build a clearer picture of your body's rhythm. As a concrete example, a period that started on January 10th, 2026 paired with a 28-day cycle points to a next period around February 7th, 2026.

The method behind those projections is well established. The calculator takes your last period's start date and adds your average cycle length to find the next one. Ovulation is placed about 14 days before that predicted period, and the fertile window covers the 5 days leading up to ovulation, ovulation day itself, and the day after, for a 6-day span in total.

Treat all of this as prediction rather than certainty, since stress, diet, and other factors can shift any given cycle. The estimate is genuinely useful, but it does not replace medical advice or finer tracking tools like basal body temperature or ovulation predictor kits. Irregular cycles weaken the predictions in particular, so feed in an average drawn from several months for the steadiest results.