Ovulation Calculator
Find your fertile days from your menstrual cycle.
Tip: Ovulation usually occurs 14 days before the next period — not 14 days after the last one.
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About this digital tool
The ovulation calculator estimates the likely day of ovulation and the fertile window from the date of your last period and your average cycle length. It also shows the date of your next period and which day of the cycle you are on today.
The calculation assumes ovulation occurs 14 days before the next period, so ovulation date = first day of period + (cycle length − 14). The fertile window starts 5 days before ovulation and ends a day after it, because sperm can survive for several days. It is an approximate estimate and works best with regular cycles. It is not a method of contraception; for family planning or difficulty conceiving, consult a gynaecologist.
How to use
- Enter the date of your last period.
- Set your average cycle length.
- See the ovulation date and the fertile window.
Frequently asked questions
How many days does the fertile window last?
About 6 days — 5 days before ovulation (sperm survive) plus the day of ovulation. Highest chance: 1–2 days before ovulation.
How is the day of ovulation calculated?
Ovulation is estimated 14 days before the next period. For a 28-day cycle it falls around day 14; for a 32-day cycle, around day 18.
Can I use this calculator as contraception?
No. Ovulation can vary from cycle to cycle and the estimate is not reliable for avoiding pregnancy. For dependable protection, talk to your doctor.
What if my cycle is irregular?
With irregular cycles the estimate is less accurate. Ovulation tests and temperature tracking can help, along with a consultation with a gynaecologist.