Ovulation & Fertility Calendar
Enter the first day of your last period and your usual cycle length. Belly Weekly maps your fertile window and likely ovulation day for the next six cycles.
General information only, not medical advice. Ask your doctor or midwife.
How this works
Formula: Ovulation = next period start − 14 days. Fertile window = the 5 days before ovulation plus ovulation day.
- Your next period is expected one cycle length after the first day of your last period.
- Ovulation usually happens about 14 days before the next period starts, so the calculator counts back 14 days.
- Sperm can live up to about 5 days and an egg about a day, so the fertile window is the 5 days before ovulation plus ovulation day. The 2 days before ovulation and the day itself are marked as peak days.
- Each later cycle simply repeats your cycle length, so the dates are estimates that get less exact the further ahead they go.
Everything is worked out in your browser. Belly Weekly does not send or store your answers.
Questions
How accurate is an ovulation calendar?
It is an estimate. It works best if your cycles are regular. Ovulation tests, tracking your temperature or cervical mucus, or advice from your doctor can give a closer read.
What if my cycles are irregular?
Use your average cycle length, but expect the dates to be less reliable. If your cycles vary a lot, talk to your doctor or midwife.
When is the best time to try to conceive?
The peak days, the 2 days before ovulation and ovulation day itself, are usually the most fertile. Having sex every 1 to 2 days across the whole fertile window covers it well.
Can I use this to avoid pregnancy?
No. A calendar alone is not a reliable way to prevent pregnancy. Ask your doctor about birth control that suits you.