Period calculator
Period calculator
Enter the first day of your last period, your cycle length and how long your period lasts to see your next six periods.
Updated
In short
How do I know when my next period will come?
Add your average cycle length to the first day of your last period. A cycle is counted from the first day of one period to the first day of the next, and most adult cycles are 24 to 38 days long. Your period then usually lasts up to 8 days. Cycles vary a little each month, so treat the date as an estimate.
Your next periods
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This is an estimate, not a diagnosis or birth control.
General information, not medical advice. Your doctor or midwife can tell you what your own results mean.
How it's calculated
- Next period = first day of last period + your cycle length.
- Each later period adds one more cycle length.
- Period end = start + your period length − 1 day.
- This assumes your cycles stay the same length. Logging a few periods shows how much yours vary.
Gyne learns your real cycle and adjusts these estimates as you log.
Frequently asked questions
How long is a normal menstrual cycle?
For most adults, 24 to 38 days, counted from the first day of one period to the first day of the next. It's common for cycle length to change by a few days from month to month.
How many days late can a period be?
A few days either way is common. If your period is more than a week late and you could be pregnant, take a pregnancy test. If you've missed three periods in a row, see a doctor.
Why are my periods irregular?
Stress, weight changes, intense exercise, breastfeeding, some medicines and conditions like PCOS or thyroid problems can all change your cycle. Ask your doctor if your cycles change suddenly or are often shorter than 24 or longer than 38 days.
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