Trying to conceive · Private
Fertile window calculator
Your fertile window is the 6 days ending on ovulation day: the 5 days before you ovulate plus the day itself. In a 28-day cycle that’s roughly days 9 to 14. Enter your dates to see yours for the next three cycles.
- No sign-up, no email needed
- Nothing you enter is stored
- Ranges that fit real, changing cycles
Your fertile windows
Enter your dates above and your estimates will show here. Nothing you enter leaves this page.
An estimate, not medical advice or birth control. Don’t use these dates to avoid pregnancy.
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What the fertile window is
About six days a cycle.
An egg lives for about a day after ovulation, and sperm can live for up to 5 days (ACOG). So pregnancy is possible from about five days before ovulation until the day after it. We estimate ovulation as 14 days before your next period, as the ovulation calculator does, and build the window around it.
Why the window looks longer here
If your cycle varies, ovulation varies with it. We include every day that could be fertile given the range you chose, so the window may be longer than six days. The middle of the range is the most likely.
Fertile window by cycle length
The fertile window shifts with your cycle length. Here are the usual days.
| Cycle length | Likely ovulation | Fertile window | Next period starts |
|---|---|---|---|
| 21 days | day 7 | days 2–7 | day 22 |
| 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 |
Days are counted from the first day of your last period (day 1). Real cycles move, so treat each as the middle of a range.
Sources: NHS: Trying to get pregnant · ACOG: Fertility awareness-based methods
How long is the fertile window?
About six days: the five days before ovulation and the day of ovulation itself. If your cycle varies, the days it falls on move too.
When is the fertile window in a 28-day cycle?
Ovulation is usually around day 14, so the fertile window is roughly days 9 to 14, counting from the first day of your period.
Can you get pregnant outside the fertile window?
It’s unlikely but possible, because ovulation can come earlier or later than expected. That’s why calendar estimates shouldn’t be used to avoid pregnancy.
How can I tell when I’m fertile?
Signs include clear, stretchy cervical mucus and a positive LH (ovulation) test. Basal body temperature rises slightly after ovulation, which confirms it has happened.
Is my data saved anywhere?
No. The calculator runs in your browser. The dates you enter are never sent to us, never put in the page address and never stored. Close the tab and they’re gone.
Can I use this as birth control?
No. These are estimates from a calendar, and ovulation can move from cycle to cycle. Don’t use them to avoid pregnancy. If you need contraception, talk to a doctor, nurse or pharmacist about methods that are tested for it.