How to use the Ovulation Calculator
- Enter the first day of your last period.
- Enter your average cycle length and period length.
- See your fertile window, ovulation date and next periods for 6 cycles.
How it works
Ovulation usually happens about 14 days before the next period starts. Sperm can survive up to 5 days and the egg about 1 day, so the fertile window is roughly the 5 days before ovulation plus the day of ovulation. With a 28-day cycle, ovulation is around day 14.
Improve accuracy
- Track your cycles for a few months to know your real average length.
- Ovulation test kits (LH tests), basal body temperature and cervical mucus changes confirm ovulation more precisely.
- Cycles can vary with stress, illness, PCOS and other conditions — talk to a gynaecologist if your cycles are very irregular.
Frequently asked questions
Can I use this as contraception?
No. Calendar-based predictions are not reliable enough to prevent pregnancy.
What if my cycles are irregular?
Use your average cycle length, but expect predictions to be less accurate. An ovulation test kit or doctor’s advice will help more.