You will get ovulation days and the fertile window for the next three cycles.
This calculator shows the approximate day of ovulation and the fertile window — the days when conception is most likely. It’s a calendar estimate based on your cycle length, not on tests. It’s a tool for planning a pregnancy, not a method of contraception — the calendar method is unreliable for preventing pregnancy.
How ovulation is calculated
- The count runs backwards from your next period. The second half of the cycle (the luteal phase) is stable for most women — about 14 days, whatever the total cycle length.
- Ovulation ≈ cycle length − 14 days from the first day of your period. On a 28-day cycle that’s day 14, on a 32-day cycle day 18, on a 24-day cycle day 10.
- The fertile window is about 6 days: the 5 days before ovulation and the day after. Sperm survive in the reproductive tract for up to 5 days, while the egg lives about 24 hours.
- The peak falls on the two days before ovulation and the day of ovulation itself.
Ovulation day by cycle length
Days are counted from the first day of your period, assuming a standard 14-day luteal phase.
| Cycle length | Ovulation day | Fertile window |
|---|---|---|
| 21 days | 7th | days 2–8 |
| 24 days | 10th | days 5–11 |
| 26 days | 12th | days 7–13 |
| 28 days | 14th | days 9–15 |
| 30 days | 16th | days 11–17 |
| 32 days | 18th | days 13–19 |
| 35 days | 21st | days 16–22 |
Ovulation FAQ
Can I use the calendar as contraception?
No. Ovulation shifts with stress, illness, travel and other factors, and sperm survive up to five days — so there are no reliably “safe” days on a calendar. For contraception you need proven methods chosen with a doctor.
My cycle is irregular — what should I do?
With an irregular cycle the calendar estimate is especially imprecise. Ovulation tests (LH strips), basal body temperature tracking and a gynaecologist’s guidance work far better — the calendar is only a rough pointer.
When should I start ovulation tests?
Usually 3–4 days before the expected ovulation — the calculator gives you that date. The test catches the LH surge, which happens roughly a day before the egg is released.
What is the luteal phase and why change it?
It’s the stretch from ovulation to your period. For most women it’s 14 days, which is the default here. Only change it if you know your own phase from tracking or medical testing.