Your next ovulation day
Your next 6 cycles
| Fertile window | Ovulation | Next period |
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Predictions assume regular cycles. Do not use this calculator as a method of contraception.
How is ovulation calculated?
Ovulation usually happens about 12 to 16 days before your next period starts. This second half of the cycle is called the luteal phase and is about 14 days for most people. The calculator works out: next period date minus your luteal phase. In a 28-day cycle that is day 14; in a 32-day cycle it is day 18.
What is the fertile window?
You can get pregnant from sex in the 5 days before ovulation and on the day of ovulation, because sperm can survive for up to 5 days and the egg lives for about a day. The calculator shows this as your fertile window, plus the day after ovulation.
Signs that you are ovulating
- Cervical mucus becomes clear, slippery and stretchy, like raw egg white.
- Ovulation test kits detect a rise in luteinising hormone (LH) about 24 to 36 hours before ovulation.
- Basal body temperature rises slightly after ovulation. It confirms ovulation has happened rather than predicting it.
When to see a doctor
If you are under 35 and have not become pregnant after 12 months of regular sex without contraception, see your doctor. If you are 35 or over, see a doctor after 6 months. See a doctor sooner if your periods are very irregular or absent.
Frequently asked questions
Can I ovulate on a different day each month?
Yes. Stress, illness, travel and changes in weight can move ovulation by a few days. Ovulation tests or tracking cervical mucus can help confirm it.
Does this work with irregular periods?
Only roughly. If your cycle length changes by more than a few days each month, the dates will be less reliable. Ovulation test kits are more useful in that case.
How often should we have sex when trying to conceive?
The NHS suggests having sex every 2 to 3 days throughout the cycle, so you do not need to time it exactly.
Can I use this to avoid pregnancy?
No. Calendar predictions are not reliable enough to use as contraception.
Is my information saved?
No. The calculation runs in your browser and nothing is stored.