worldofcalcsOvulation Calculator
Usually 28 days
Most Fertile Window
Thu, 22 Oct, 2026 – Wed, 28 Oct, 2026
Estimated Ovulation
Tue, 27 Oct, 2026
Next Period Starts
Tue, 10 Nov, 2026
When do you ovulate?
Ovulation, when an ovary releases an egg, usually happens about 14 days before your next period. You are most likely to conceive in the fertile window: the five days before ovulation and the day of ovulation itself, because sperm can survive for up to five days. This calculator estimates those days from your last period and cycle length.
How ovulation is estimated
Ovulation ≈ first day of last period + (cycle length − 14) days
The phase after ovulation is fairly constant at about 14 days, so a longer cycle means later ovulation. The fertile window runs from 5 days before ovulation to 1 day after. Your next period is expected one cycle length after the last one began.
Getting a better estimate
- Cycles vary from month to month, so treat the dates as a guide. Tracking a few cycles gives a better average length.
- Ovulation test kits, which detect the LH surge 24–36 hours before ovulation, and changes in cervical mucus or basal body temperature help confirm the timing.
- Having sex every 1–2 days during the fertile window gives the best chance of conceiving.
- This calculator is not a reliable method of contraception.
- See a doctor if your cycles are often shorter than 21 days or longer than 35, if periods are irregular, or if you haven't conceived after a year of trying (6 months if you are over 35).
- This calculator gives estimates for information only and is not a substitute for advice from a doctor.
Worked example
- Last period started on 1 October 2026; cycles are usually 28 days
- Ovulation: 1 October + 14 days = around 15 October
- Fertile window: about 10 to 16 October
- Next period expected around 29 October
- With a 32-day cycle, ovulation moves 4 days later, to around 19 October
Ovulation by cycle length
Estimated dates for a period that started on 1 October 2026.
| Cycle length | Ovulation | Fertile window | Next period |
|---|---|---|---|
| 21 days | 8 Oct | 3 Oct – 9 Oct | 22 Oct |
| 24 days | 11 Oct | 6 Oct – 12 Oct | 25 Oct |
| 26 days | 13 Oct | 8 Oct – 14 Oct | 27 Oct |
| 28 days | 15 Oct | 10 Oct – 16 Oct | 29 Oct |
| 30 days | 17 Oct | 12 Oct – 18 Oct | 31 Oct |
| 32 days | 19 Oct | 14 Oct – 20 Oct | 2 Nov |
| 35 days | 22 Oct | 17 Oct – 23 Oct | 5 Nov |
Ovulation is about 14 days before the next period, whatever your cycle length.