Ovulation Calculator
Estimate your ovulation date and most fertile days from your last period and average cycle length.
Reviewed by the OmniCalc teamMethod verified 2026-07-01
January 15, 2026estimated ovulation
= fertile window January 10, 2026 – January 16, 2026= next period January 29, 2026
Estimated ovulation January 15, 2026An estimate based on your average cycle — real ovulation can vary. Informational only, not medical advice.
Show steps
- Next period ≈ last period + 28-day cycle = 2026-01-29.
- Ovulation ≈ next period − 14 days (luteal phase) = 2026-01-15.
- Fertile window = ovulation − 5 to +1 day = 2026-01-10 to 2026-01-16.
How to use the ovulation calculator
- 1Enter the first day of your last period.
- 2Adjust the cycle length if yours isn’t 28 days.
- 3Read your estimated ovulation date and fertile window.
An estimate, not a diagnosis
This is a rule-of-thumb date based on an average cycle — real ovulation can shift, especially with an irregular cycle. For anything you’re planning around conception or contraception, talk to a doctor. This isn’t medical advice.
Frequently asked questions
How is ovulation estimated?
The luteal phase (from ovulation to the next period) is fairly constant at about 14 days. So ovulation is estimated as your next expected period — last period plus your cycle length — minus 14 days.
What is the fertile window?
The days you're most likely to conceive: roughly the five days before ovulation plus ovulation day itself, because sperm can survive up to about five days and the egg lives about a day after release.
How accurate is it for an irregular cycle?
It assumes a regular cycle of the length you enter, so an irregular or unpredictable cycle makes the estimate far less reliable. Tracking basal body temperature or using an ovulation predictor kit gives a more personal signal.