TooldenTOOLDENEVERYDAYON-DEVICE
Ovulation Calculator
Estimate your fertile window, ovulation day and next period date. Enter your last menstrual period and average cycle length, all computed in your browser.
HOW TO USE
- 1Pick the first day of your last period (LMP) with the date picker.
- 2Enter your average cycle length in days (21 to 35).
- 3Read the 5-day fertile window, ovulation day and next period date in the results.
EXAMPLE
INPUT
LMP: January 1, 2025 · Cycle length: 28 days
OUTPUT
Fertile window: January 11 to 15, 2025 · Ovulation: January 15 (day 14) · Next period: January 29, 2025
FAQ
What is the fertile window?
The fertile window is the 5 days ending on ovulation day. Sperm can survive up to 5 days in the reproductive tract, so intercourse in this window has the highest chance of conception.
How accurate is this calculator?
It uses the standard method: ovulation occurs about 14 days before your next period starts. Cycle lengths vary from month to month, so the result is an estimate, not a guarantee.
My cycle length varies. What should I enter?
Enter your average cycle length over the last few months. If your cycles are consistently outside 21 to 35 days, speak with a healthcare provider.
Can I use this to avoid pregnancy?
No. Calendar-based prediction is not a reliable method of contraception. Use this only for planning or understanding your cycle, and consult a healthcare professional.
Why is my fertile window 5 days?
Sperm can survive about 5 days, while the egg lives only about 24 hours after release. The 5-day window ending on ovulation day captures the days intercourse is most likely to lead to conception.