Menstrual Cycle Calculator: Next Period Dates
Estimate your next period, your current cycle day and the periods ahead from your last period and cycle length. A quick estimate, with nothing stored.
Estimate your next period, your current cycle day and the periods ahead from your last period and cycle length. A quick estimate, with nothing stored.
Your next period
Pick your last period date
Add a date to see where you are in your cycle.
These are estimates that assume a steady cycle. Length naturally varies month to month. If your periods are very irregular, unusually heavy or have stopped, it is worth checking in with a doctor: see our guides to PMS and perimenopause. This tool is information, not medical advice.
How it works
Enter the first day of your last period and your cycle length to see your next period, your current cycle day, and the next few period dates.
The formula and sources
It counts forward from your last period by your cycle length to project the dates, and works out where you are in the current cycle from today's date.
Assumptions
- Your cycle length is fairly steady.
- Dates are entered accurately.
Limitations
These are estimates that assume a regular cycle. Length naturally varies from month to month, so treat the dates as a guide.
When to see a doctor
If your periods are very irregular, unusually heavy, or have stopped, it is worth checking with a doctor. See our guides to PMS and perimenopause.
Primary sources
- NHS, Periods. For most women a period comes around every 28 days, though anywhere from every 21 to every 35 days is common. A period usually lasts about five days, within a range of two to seven.
Calculator version 1.0. Figures and formula last checked 27 July 2026 against the sources above. This tool gives general information and does not replace advice from your own doctor.
Frequently asked questions
How do I calculate my next period?
Count forward from the first day of your last period by your average cycle length. The tool does this and projects the next few dates for you.
What is a normal cycle length?
Anywhere from about 21 to 35 days is normal, and some variation from month to month is expected.
Why is my period late?
Stress, illness, travel, weight change, perimenopause and pregnancy can all delay it. An occasional late period is common.
When should I see a doctor about my cycle?
If periods stop, become very irregular, or are unusually heavy or painful. See our guides to PMS and perimenopause.