Ovulation Calculator
Estimate when you're most likely to ovulate based on your last period and cycle length. Shows your fertile window - the days when conception is most likely.
How to use
- Enter the first day of your last period.
- Enter your usual cycle length. If it varies, use your average.
- You'll see your estimated ovulation date and the fertile window around it.
Related tools:
Ovulation typically occurs around 14 days before the next period - not 14 days after the last one, which is a common mix-up. For a 28-day cycle, that lands on day 14. For a 32-day cycle, it is day 18. The fertile window is the 5 days before ovulation plus the day of ovulation itself - sperm can survive up to 5 days, so intercourse in the days leading up to ovulation can still result in conception.
Cycles are not perfectly regular for most people. Stress, illness, travel, and weight changes can shift ovulation by several days. This calculator gives you an estimate based on your average cycle length, but it is most accurate when your cycles are consistent. If you are actively trying to conceive, tracking basal body temperature or using LH surge tests gives more reliable day-of-ovulation confirmation.
Frequently Asked Questions
What is the most fertile day?
The day of ovulation and the day before are when fertility is highest. Since the egg only survives 12-24 hours after release, the window is narrow. Sperm, however, can wait for ovulation if intercourse occurs a few days before.
Can I use this calculator to avoid pregnancy?
No. The fertility awareness method has a high failure rate without rigorous daily tracking, training, and consistent cycles. This calculator is not a contraceptive tool - it is an estimate for informational or conception-planning purposes only.
What if my cycle length varies month to month?
Variable cycles make ovulation harder to predict by calendar alone. If your cycle varies by more than 5-7 days regularly, consider combining calendar estimates with temperature charting or LH ovulation test strips for more reliable timing.