About the Ovulation Calculator
Ovulation usually happens about 14 days before your next period. Your fertile window is the 6 days ending on ovulation day. This calculator estimates both for your next three cycles.
How to use the Ovulation Calculator
- Enter the first day of your last period.
- Enter your average cycle length and period length.
- See your fertile window and ovulation date for upcoming cycles.
- Track signs like cervical mucus or use ovulation kits for more accuracy.
Formula used
Next period = last period start + cycle length. Ovulation ≈ next period − 14 days. Fertile window = ovulation day − 5 days to ovulation day (plus the day after).
Frequently asked questions
What are my most fertile days?
The two to three days before and including ovulation day have the highest chance of pregnancy.
Can I use this as birth control?
No. Cycle-based estimates are not reliable enough for contraception.
Does stress affect ovulation?
Yes. Stress, illness, travel, weight change and conditions like PCOS can shift or delay ovulation.
Last reviewed: November 7, 2026