Ovulation calculator
Your likely ovulation day and most fertile days for the next few cycles.
- 100% free
- No sign-up
- Runs in your browser
How to use Ovulation calculator
- Enter your last period
- See your fertile window
- Plan ahead
Your cycle
From the first day of one period to the day before the next. 28 is typical.
Estimated ovulation
Pick the first day of your last period to see your fertile days.
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How to use Ovulation calculator
Enter your last period
Pick the first day of your last period, then your usual cycle length (21 to 45 days) and how long your period lasts.
See your fertile window
Get your estimated ovulation day, your six most fertile days and when your next period should start.
Plan ahead
Look through a calendar and a list of the next three or six cycles, and copy the dates if you want to keep them.
Why use Utils365
Calendar view
Period, fertile and ovulation days are coloured on a month calendar you can page through.
Up to six cycles
See the coming months at a glance, with each period, fertile window and ovulation day listed.
Any cycle length
Works for cycles from 21 to 45 days, placing ovulation about 14 days before the next period.
Private
Cycle dates are sensitive. Here they’re worked out in your browser and never sent or stored.
Frequently asked questions
How do I calculate my ovulation day?
Take your cycle length and subtract 14. With a 28-day cycle you’ll likely ovulate on day 14; with a 32-day cycle, around day 18, counting the first day of your period as day 1.
What is the fertile window?
The six days that end on ovulation day. Sperm can live up to five days, and an egg about a day, so sex in those days gives the best chance of pregnancy.
When am I most likely to get pregnant?
The two days before ovulation and ovulation day itself. Studies show the chance of conceiving is highest from sex one to two days before ovulation.
Can I use this as contraception?
No. Cycles vary month to month, and ovulation can come early or late, so calendar dates can’t tell you when you’re safe. Use a reliable method of contraception.
What if my periods are irregular?
Calendar estimates are less reliable when cycles vary by more than a few days. Ovulation test kits, cervical mucus checks or basal body temperature tracking give a better picture.
When should I take a pregnancy test?
Most tests are reliable from the day your period is due, about 14 days after ovulation. Testing earlier can give a false negative.