Predict your next period and see your estimated cycle dates. Based on date math only — not a fertility or contraception tool.
A normal menstrual cycle is 21–35 days long (measured from day 1 of one period to day 1 of the next). Most cycles are around 28 days. A period (menstrual bleeding) typically lasts 2–7 days.
It's normal for cycles to vary by a few days from month to month. Cycles can be more irregular in the first few years after periods start (menarche) and in the years leading up to menopause (perimenopause).
A period is generally considered late if it hasn't arrived within 7 days of the expected date. Many things can delay a period temporarily:
If your period is more than 7 days late and there is any possibility of pregnancy, take a pregnancy test. If more than 3 weeks late with a negative test, see your GP.
Your cycle length is the number of days from the first day of one period to the first day of the next period. It does not include the duration of your period — just the gap between starts.
Example: Period starts 1 March, next period starts 29 March → cycle length is 28 days.
For the most accurate result, track 3–6 cycles and average them. A single cycle can vary by a few days and may not represent your typical pattern.
Ovulation is the release of an egg from the ovary. It typically occurs around 14 days before the next expected period — not necessarily 14 days after the last period. For a 28-day cycle this is usually around day 14; for a 35-day cycle it's closer to day 21.
The fertile window is roughly the 5 days before ovulation plus the day of ovulation itself — about 6 days total when pregnancy is most likely.
Important: The calendar/rhythm method is not a reliable form of contraception. Cycles vary, ovulation can shift, and sperm can survive several days. Speak to your GP about contraception options.
See your GP if: