Project your next several periods and cycle phases from your history.
A menstrual cycle begins on the first day of bleeding and ends the day before the next period. Tracking your average cycle length lets you project future periods and fertile windows, which is useful for planning, recognising late periods, or identifying cycle irregularities.
Next period
Next period start = LMP + cycle length
This calculator is an estimate based on average cycle patterns. It is not a reliable contraceptive method. Consult a healthcare provider for personalised reproductive health advice.
A typical menstrual cycle is 24–38 days, with 28 days being the textbook average. Cycles shorter than 21 days or longer than 45 days may warrant investigation by a healthcare provider.
Many factors can shift ovulation — and therefore the next period — including stress, illness, significant weight change, intensive exercise, travel, hormonal contraceptives, or pregnancy. One late period is rarely cause for alarm, but a consistent pattern of irregular cycles is worth discussing with a doctor.
This calculator can help you identify fertile windows for conception or, if combined with OPKs and BBT charting, as part of fertility awareness-based methods for avoiding pregnancy. Calendar methods alone have a higher failure rate than hormonal contraceptives.