Period Calculator

Use it for simple educational checks, trend tracking, or planning tasks like these: Estimate the next upcoming period start date from an older or recent last-period entry. Estimate the expected end date from period length. It can help you understand a number, but it cannot explain your whole health situation.

Enter the first day of the last period, your usual cycle length from one period start to the next, and period length in bleeding days. Use the start date, not the last day of bleeding. If cycles vary, use a recent average and read the answer as a planning estimate for regular-ish cycles.

In plain language: Next period start = last period start plus cycle length. If that predicted start is not in the future, the calculator keeps adding cycle length until it reaches the next upcoming start. Expected end = next period start plus period length minus 1 day. Following periods add cycle length again. Read the result together with the notes on the page, because health and fitness numbers often need personal context.

Read the next start, expected end, following period, and third period as calendar estimates. The calculator keeps adding cycle length until it reaches the next predicted start in the future, then uses period length only to estimate the end date. Stress, illness, medication changes, postpartum changes, travel, and normal variation can move real dates.

The live result is meant to show the next upcoming predicted start. If the first cycle after the last period is already in the past, the calculator keeps adding the cycle length until the predicted start is still ahead of today.

Use period start to period start. Cycle length means the number of days from the first day of one period to the first day of the next. Period length means how many bleeding days to use when estimating the expected end date.

Cycle length controls the next start date. Period length only estimates the expected end by counting from the predicted start. A longer period does not automatically mean the next cycle starts later.

Use the result as a rough planning note only. Calendar predictions are less reliable when cycle length changes a lot, periods are missing, birth control recently changed, postpartum cycles are returning, or stress, illness, travel, or medication affects timing.

No. Period prediction is not contraception and does not confirm ovulation. If pregnancy prevention matters, use a reliable contraceptive method and qualified medical guidance instead of a calendar estimate.

This calculator cannot diagnose pregnancy, hormone changes, stress effects, illness, medication effects, or other causes of a late or missing period. Consider an appropriate pregnancy test or qualified care if the timing matters or symptoms are concerning.

This is an educational calendar estimate, not medical advice, contraception, a fertility test, a pregnancy test, or a diagnosis for late, missed, heavy, painful, or irregular periods. Use the calculator as a learning tool, then ask a qualified professional about decisions that affect care, pregnancy, medication, nutrition, or safety.

Check that the date is the first day bleeding started, that cycle length means start-to-start, and that period length means the number of bleeding days. Do not enter an ovulation date, expected end date, positive test date, or cycle-day number into the last-period field.

No. The calculator runs in your browser tab. Recent answers stay only on the page while you use it, and they are not sent to a server.