A period calculator is an online tool that predicts your next menstrual period date based on your last period and average cycle length.

You input the first day of your last period and your average cycle length. The calculator then estimates future period dates using menstrual cycle patterns.

Yes, it is mostly accurate for women with regular cycles. Accuracy may vary if cycles are irregular or affected by stress, illness, or hormonal changes.

Accuracy is usually 85–95% for regular cycles. It may be less accurate for irregular periods.

Your next period usually comes 28 days after your last period, but this can vary from 21 to 35 days depending on your individual cycle.

You should expect your period around the date predicted by the calculator, depending on your cycle length.

Your period is due based on your last cycle. Enter your last period date into the calculator to know the exact due date.

Your last period is counted from the first day of bleeding, not spotting.

Period length is the number of days you bleed, usually 3 to 7 days.

A regular cycle is typically 21–35 days long and happens consistently each month.

If your periods are irregular, predictions may vary. Tracking for 3–6 months improves accuracy.

It predicts the fertile window and ovulation day, usually 14 days before your next period.

It calculates ovulation using cycle length and period start date.

It identifies days when pregnancy is most likely (fertile window).

Usually 5 days before ovulation + ovulation day.

Yes. It helps estimate fertile days and missed periods, which may indicate pregnancy.

If your period is late beyond the predicted date, pregnancy is possible. A pregnancy test is recommended.

It estimates pregnancy weeks based on the last menstrual period (LMP).

No. It only predicts dates. Pregnancy must be confirmed with a test.

You should test 5–7 days after a missed period for accurate results.