Ovulation & Fertile Window Calculator
Estimate when you ovulate and which days you are most likely to conceive, based on your own cycle length rather than a generic day-14 assumption.
Count from day 1 of one period to day 1 of the next
14 days is typical and fairly consistent
Ovulation day
Tue, 8 Sept, 2026
Most fertile window
Thu, 3 Sept, 2026 to Wed, 9 Sept, 2026
6 days with the highest chance
Next period expected
Tue, 22 Sept, 2026
| Cycle | Fertile window | Ovulation | Test from |
|---|---|---|---|
| This cycle | Thu, 3 Sept, 2026 – Wed, 9 Sept, 2026 | Tue, 8 Sept, 2026 | Sun, 20 Sept, 2026 |
| +1 cycle | Thu, 1 Oct, 2026 – Wed, 7 Oct, 2026 | Tue, 6 Oct, 2026 | Sun, 18 Oct, 2026 |
| +2 cycles | Thu, 29 Oct, 2026 – Wed, 4 Nov, 2026 | Tue, 3 Nov, 2026 | Sun, 15 Nov, 2026 |
Ovulation is calculated by counting the luteal phase back from the next expected period, which is more reliable than the old day-14 rule because the luteal phase stays fairly constant while cycle length varies. The fertile window covers the five days before ovulation plus the day after, since sperm survive up to five days but the egg only about one. Cycles vary month to month, so this is an estimate — it is not a reliable method of contraception, and a doctor is the right person to consult about fertility.
Frequently Asked Questions
When does ovulation actually happen?
About 14 days before your next period, not 14 days after the last one. That distinction matters: the luteal phase after ovulation stays fairly constant, while the follicular phase before it varies, so a 32-day cycle means ovulation around day 18.
How long is the fertile window?
About six days: the five days before ovulation plus the day of ovulation itself. Sperm survive up to five days in the reproductive tract, while the egg is viable for only 12 to 24 hours.
Can I use this as contraception?
No. Cycles vary month to month, ovulation can shift with stress or illness, and the calculation is only an estimate. Use a proper contraceptive method if you are trying to avoid pregnancy.
What signs indicate ovulation?
Cervical mucus becoming clear and stretchy like egg white, a slight rise in basal body temperature after ovulation, and a positive result on an ovulation predictor kit which detects the LH surge 24 to 36 hours beforehand.
When can I take a pregnancy test?
From about 12 days after ovulation, shown in the table above. Testing earlier often gives a false negative because implantation may not yet have produced enough hCG to detect.