Predict your next 3 period dates and fertile windows based on your cycle.
Keeping track of your period doesn't have to mean remembering exact dates or digging through your phone for an app. Enter your last period start date and your average cycle length, and this calculator shows you when your next period is expected, when your fertile window falls, and a three-month calendar of predicted dates.
It's useful for planning around events, travel, or anything else that's easier to manage when you know what's coming. The predictions are based on averages — actual timing can shift with stress, illness, travel across time zones, changes in weight or exercise, and hormonal changes.
Tracking your actual cycle over a few months gives you a more accurate average to work with and makes the predictions more reliable.
A typical cycle runs 21-35 days, with 28 days being the statistical average. Cycles shorter than 21 days or longer than 35 days consistently may be worth discussing with a GP.
Cycle length varies naturally from month to month for most people, affected by stress, sleep changes, diet, exercise levels, illness, and hormonal fluctuations. A variation of a few days either way is completely normal. Consistent changes or very irregular cycles are worth mentioning to a doctor.
A period is generally considered late if it hasn't arrived within 5-7 days of the expected date based on your typical cycle. If you're sexually active and your period is late, a pregnancy test is the obvious first step. Other causes of late or missed periods include stress, significant weight change, illness, and thyroid issues.
Most periods last between 3 and 7 days, with the heaviest flow in the first two days. Periods consistently shorter than 2 days or longer than 8 days, or that are much heavier than usual, are worth discussing with a GP.