Fertile Window Calculator
Your fertile days and chance of pregnancy today. Free, private and instant.
How to use the Fertile Window
- Pick first day of your last period.
- Enter average cycle length (days).
- Choose luteal phase (ovulation to next period): 10 days, 11 days, 12 days, 13 days and more.
- Press Calculate to get an instant result with a colour scale, chart and plain-English explanation.
About the Fertile Window
Your fertile window is the 6 days when pregnancy is possible: the 5 days before ovulation and the day of ovulation. This calculator shows your next three windows, how likely pregnancy is today, and highlights the peak days.
Also known as: fertile days calculator, fertility window, when am I most fertile, best days to get pregnant.
Worked example
Dates in this example are worked out as if today were 5 Nov 2026.
- First day of your last period: 22 Oct 2026
- Average cycle length: 28 days
- Luteal phase (ovulation to next period): 14 days (typical)
Chance of pregnancy today (per act): 33 % (You are in your fertile window). Your next fertile window is 31 Oct - 6 Nov 2026, with ovulation around 5 Nov 2026. You are in your fertile window.
- Next fertile window: 31 Oct - 6 Nov 2026
- Ovulation: 5 Nov 2026
- Window after that: 28 Nov - 4 Dec 2026
- Third window: 26 Dec - 1 Jan 2027
Formula and cut-offs
Fertile window = ovulation day - 5 to ovulation day + 1. Ovulation = next period - luteal phase (14 days by default). Sperm live up to 5 days; the egg lives about 24 hours.
Frequently asked questions
How long is the fertile window?
About 6 days each cycle: the 5 days before ovulation and ovulation day.
Can I get pregnant on my period?
It is uncommon but possible, especially with short cycles, because sperm can survive for days.
What are the best days to conceive?
The 2 days before ovulation and the day of ovulation have the highest chance.
When is my fertile window if my last period started on 22 Oct 2026 and my cycle is 28 days?
Your next fertile window is 31 Oct - 6 Nov 2026, with ovulation around 5 Nov 2026. You are in your fertile window. This example treats 5 Nov 2026 as today. Enter your own dates above for a personal result.
Sources and references
Written and checked by the MediHub editorial team against the sources above. Read how we build and review our calculators.
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Last updated . This calculator is for education only and is not medical advice. See the medical disclaimer.