period tools

Next Period Calculator

Find out exactly when your next period will start. Enter the first day of your last period and your cycle length — we’ll show you the next six expected start dates in seconds.

Pick the date your most recent period started.

21 days45 days

Days from one period's first day to the next. Most cycles are 21–35 days.

1 days10 days

How many days bleeding usually lasts.

Pick the first day of your last period to see your next 6 cycles.

How the Next Period Calculator works

The math is straightforward: last period start + cycle length = next period start. If your last period began on June 1st and your cycle is 28 days, your next period is expected around June 29th. We project six future cycles so you can plan around vacations, events, or anything else where knowing your dates matters.

Cycle length is the number of days between the first day of one period and the first day of the next. The 28-day cycle people quote so often is closer to a textbook average than a rule — most cycles fall anywhere between 21 and 35 days. Use the slider to dial in your personal length.

The earlier you can enter your average instead of a default, the better the predictions get. Three or four months of tracking is enough to spot your pattern.

When your next period date can shift

Cycles are sensitive. Common reasons predictions drift by a few days:

  • Stress, big sleep changes, or new travel time zones
  • Recent illness or new medication
  • Coming off hormonal contraception
  • Major changes in weight or exercise volume
  • Breastfeeding or being recently postpartum

One unusual cycle is normal. A pattern of unusual cycles is worth a chat with your healthcare provider.

Frequently asked questions

How do I calculate when my next period will start?
Take the first day of your last period and add your average cycle length in days. If your last period started on the 1st and your cycle is 28 days, your next period is expected around the 29th. Our Next Period Calculator does this for you instantly, including a six-cycle preview so you can plan months ahead.
What is the average cycle length?
Most adult cycles fall between 21 and 35 days, with the classic 28-day cycle being the textbook average rather than an iron rule. Track three to six cycles in a row to learn your personal average and use that number for the most accurate predictions.
Why is my next period not arriving on the predicted date?
Cycles shift naturally with stress, travel, illness, sleep changes, weight changes, exercise intensity, and hormonal contraception. A prediction within two or three days of the actual date is considered good. If your period is more than seven days late and pregnancy is possible, consider taking a test.
How many days late is too late?
Up to seven days past the expected date is usually considered within the normal range for an occasional cycle. Beyond that — especially repeated months in a row — it is worth checking in with a healthcare provider. See our companion Late Period Calculator for a focused view on how late your period is and what that can mean.
Does this calculator store my data?
No. Calculations run in your browser only. Nothing is sent to a server, saved to a database, or shared with anyone. Refreshing the page clears your inputs.

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