A free period calculator is an online tool that estimates when your next period may start using the first day of your last period and your average menstrual cycle length. Many calculators also provide estimated ovulation and fertile-window dates.

A period calculator uses your last period start date and typical cycle length to estimate your next menstrual period. Depending on the calculator, it may also estimate your ovulation date, fertile window, and other cycle dates.

To estimate your next period, count your usual menstrual cycle length from the first day of your most recent period. For example, if your typical cycle is 28 days, your next period may be estimated about 28 days after the previous period began.

A free period calculator can estimate ovulation from your expected next period and average cycle length. Ovulation is often estimated at about 14 days before the next period, but the timing can vary between cycles, so the result should be treated as an estimate.

The fertile window is the part of the menstrual cycle when pregnancy is more likely to occur. It generally includes the days leading up to ovulation and the day of ovulation. A period calculator can provide an estimated fertile window based on cycle information.

A free period calculator provides an estimate rather than an exact prediction. Results may be more consistent when your menstrual cycles follow a similar pattern. Stress, illness, hormonal changes, and other factors can affect cycle timing.

Yes. You can use a period calculator with irregular cycles, but predicted dates may be less precise when your cycle length changes from month to month. Tracking several cycles can help you understand your usual pattern.

No. A late period can have several possible causes, including changes in stress, illness, routine, hormones, or pregnancy. A period calculator can estimate cycle dates, but it cannot determine why your period is late.

A pregnancy due date can be estimated from the first day of the last menstrual period. A standard estimate is about 40 weeks, or 280 days, from that date. A healthcare professional can provide a more individualized assessment.

Consider speaking with a healthcare professional if you have persistent cycle changes, unusually heavy bleeding, severe pain, or other symptoms that concern you. A period calculator is useful for estimates but does not replace professional medical advice.