Estimate your upcoming periods. This free menstrual cycle calculator uses your last period and average cycle length to project your next dates — a simple general tracker, not a contraceptive or medical tool.
⚠ This is a general cycle-tracking estimate only. It is not a contraceptive, fertility treatment, or medical tool. Cycles vary naturally — do not rely on it to prevent or plan pregnancy. For anything health-related, talk to a healthcare professional.
Your cycle
days
days
A typical cycle is around 21–35 days. Enter your own average for a closer estimate.
Estimated next period
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Enter your last period date
Period after that
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Estimated ovulation
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Estimated fertile window
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Cycle day today
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These dates are rough estimates based on a regular cycle. Real cycles shift with stress, health and many other factors. Not for contraception or medical decisions.
Use this free menstrual cycle calculator to estimate your next period dates from your last period and average cycle length. It’s a simple general tracker to help you anticipate upcoming cycles.
Please read first: this calculator is a general tracking estimate only. It is not a contraceptive, fertility treatment, or medical tool, and should never be used to prevent or plan a pregnancy or to make health decisions. Cycles vary naturally from month to month. For anything health-related, speak with a healthcare professional.
What this menstrual cycle calculator shows you
A menstrual cycle calculator uses the first day of your last period and your average cycle length to estimate your next couple of period dates, an approximate ovulation date and a rough fertile window. It assumes a regular cycle, so the dates are estimates, not predictions.
How the estimates are calculated
Your next period is estimated by adding your average cycle length to the first day of your last period. Ovulation is approximated as about 14 days before the next expected period, and the fertile window as the few days around it. With a last period of June 1 and a 28-day cycle, the next period would fall around June 29.
Understanding your cycle
Phase
Roughly when
Menstruation
The days you bleed, at the start of the cycle.
Follicular phase
From the first day of your period until ovulation.
Ovulation
Around the middle of a regular cycle.
Luteal phase
From ovulation to the next period.
A typical cycle runs about 21–35 days and varies between people and from month to month.
How to use the menstrual cycle calculator
Enter the first day of your last period.
Add your average cycle length (the default is 28 days).
Add your typical period length if you’d like.
Read the estimates. Upcoming dates appear instantly.
Why cycles vary
Stress, illness and travel can shift timing.
Sleep, weight changes and exercise all play a role.
Hormonal changes across life stages affect regularity.
Because of this, no calculator can predict a cycle precisely — track over time for a better personal average.
Menstrual Cycle FAQ
How do I calculate my next period?
Add your average cycle length to the first day of your last period. With a 28-day cycle and a last period starting June 1, the next would be expected around June 29. Real timing varies, so treat it as an estimate.
How long is a normal menstrual cycle?
A typical cycle is about 21 to 35 days, counted from the first day of one period to the first day of the next. It can differ between people and from one month to the next.
Can I use this calculator for contraception?
No. This is a general tracking estimate only and must never be used to prevent or plan pregnancy. Cycles vary too much to rely on for contraception — speak with a healthcare professional about suitable methods.
How accurate are the estimates?
They assume a regular cycle, so they're rough guides rather than predictions. Stress, illness, travel and many other factors can shift your actual dates. Tracking over several months gives a better personal average.
What is the fertile window shown here?
It's an approximate range around the estimated ovulation date, based on a regular cycle. It's for general awareness only and is not reliable for planning or avoiding pregnancy.
Is the menstrual cycle calculator free to use?
Yes, this menstrual cycle calculator is completely free, needs no sign-up, and gives instant results directly in your browser.
