Ovulation Calculator
HEALTHEstimate your ovulation window and most fertile days from your cycle length and last period. Free ovulation estimator.
Enter your details and click Calculate
ℹ️ About Ovulation Calculator
An ovulation calculator estimates when you are most likely to ovulate — and therefore your most fertile days — based on the date of your last period and your average cycle length. Ovulation typically happens about 14 days before your next period starts, and the fertile window spans the few days leading up to and including it. This is a planning estimate, not medical advice.
📖 How to Use Ovulation Calculator
1
Enter your last period date
The first day of your most recent period.
2
Enter your cycle length
Your average number of days from one period to the next (often 28).
3
Get your estimate
See your estimated ovulation day and fertile window.
4
Plan ahead
Use the window to time trying to conceive, or simply to understand your cycle.
💡 Examples
Average cycle
INPUT
28-day cycle, period Jan 1→
OUTPUT
Ovulation ~Jan 15; fertile ~Jan 11–16Longer cycle
INPUT
30-day cycle, period Jan 1→
OUTPUT
Ovulation ~Jan 17; fertile ~Jan 13–18Shorter cycle
INPUT
26-day cycle, period Jan 1→
OUTPUT
Ovulation ~Jan 13; fertile ~Jan 9–14📊 Estimated Ovulation Day by Cycle Length
Ovulation is about 14 days before the next period, so it depends on your cycle length (counting from the first day of your last period):
| Cycle length | Approx. ovulation day | Approx. fertile window |
|---|---|---|
| 24 days | Day 10 | Days 6–11 |
| 26 days | Day 12 | Days 8–13 |
| 28 days | Day 14 | Days 10–15 |
| 30 days | Day 16 | Days 12–17 |
| 32 days | Day 18 | Days 14–19 |
Estimates for regular cycles. Individual timing varies — not medical advice.
🚀 Pro Tips
✓Ovulation is estimated at about 14 days before your next period, so it shifts with your cycle length — not always "day 14".
✓The fertile window is roughly the 5 days before ovulation plus the ovulation day, because sperm can survive several days.
✓Cycles vary month to month; track a few to find your real average for a better estimate.
✓Signs like a basal body temperature rise or cervical mucus changes can confirm ovulation alongside the estimate.
✓This is an estimate for planning, not a contraceptive method and not medical advice.