Ovulation Calculator
Calculate your estimated ovulation date, fertile window, and next period date. Covers 3 upcoming cycles. Enter your last period start date and average cycle length.
Ovulation & Fertile Window Calculator
LMP + cycle length → ovulation · fertile window · next period
Calendar-based prediction. For irregular cycles, supplement with OPK tests and BBT charting. Not a substitute for medical advice. This tool should not be used for contraception.
Ovulation is estimated as: Cycle Start Date + (Cycle Length − Luteal Phase Length). The fertile window is the 5 days before ovulation plus ovulation day itself — days when conception is possible. Results show 3 consecutive cycles.
Ovulation Day by Cycle Length
| Cycle Length | Ovulation Day | Fertile Window (Cycle Days) | Next Period |
|---|---|---|---|
| 24 days | Day 10 | Days 5–10 | Day 25 |
| 26 days | Day 12 | Days 7–12 | Day 27 |
| 28 days | Day 14 | Days 9–14 | Day 29 |
| 30 days | Day 16 | Days 11–16 | Day 31 |
| 32 days | Day 18 | Days 13–18 | Day 33 |
| 35 days | Day 21 | Days 16–21 | Day 36 |
How to Increase Conception Chances
The most important factor in optimising conception timing is identifying the fertile window accurately. Research shows that having sex every 1–2 days during the 5-day fertile window (5 days before ovulation and ovulation day) provides the highest probability of pregnancy per cycle. For couples who prefer to focus on peak days: the day of ovulation and the day before are the highest-probability days. Combining calendar tracking with OPK testing (which detects the LH surge 24–36 hours before ovulation) and cervical mucus observation significantly improves prediction accuracy over calendar methods alone. Lifestyle factors — maintaining healthy body weight, limiting alcohol, stopping smoking, managing stress — all improve fertility outcomes. Men's sperm quality is also significantly affected by heat, tight underwear, smoking, and excessive alcohol.