Ovulation Calculator
NEWEstimate your ovulation date and fertile window from your cycle. For information only, not medical advice.
How to use Ovulation Calculator
For information only, not medical advice.
- Enter the first day of your last period and your typical cycle length.
- Your estimated ovulation date and fertile window are calculated automatically.
Frequently asked questions
How is ovulation date calculated?
It predicts your next period (last period start date plus your cycle length), then counts back 14 days — the typical length of the luteal phase (the second half of the cycle, from ovulation to the next period), which stays fairly constant even when overall cycle length varies.
What is the 'fertile window'?
The 6-day span from 5 days before predicted ovulation through 1 day after — reflecting that sperm can survive a few days in the body while the egg is viable for about a day after release, making this the window where conception is most likely.
Can I rely on this for contraception?
No — the tool explicitly notes it's a general estimate based on average cycle patterns, not a reliable contraception method. Actual ovulation timing varies cycle to cycle even for people with regular periods.
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