Ovulation & Fertile Days Calculator Online: Free 2026
Estimate your fertile days, ovulation day and next period from your cycle.
Estimate your ovulation day and fertile window from your last period and cycle length. Useful as a planning reference — no guarantees.
By VOV · Last updated: October 21, 2026
Guidance estimate for regular cycles. Not a reliable contraceptive method and not a substitute for medical advice.
Use cases
- Pinpoint your most fertile days this month if you're trying to get pregnant this year
- Calculate your next ovulation window to schedule your fertility visits with the gynecologist in advance
- Find your fertile window to practice natural family planning methods with much greater precision this cycle
Frequently asked questions
How are fertile days calculated?
Ovulation happens about 14 days before the next period. The fertile window covers the 5 previous days plus ovulation day, since sperm survive up to 5 days.
Does it work with irregular cycles?
With caveats: the math assumes regular cycles. If yours vary a lot, the result is less reliable; consult your doctor.
Can I use it as contraception?
No. The rhythm method has a high failure rate. Do not use this calculator to avoid pregnancy.