Quick answer
When am I most fertile?
You’re most fertile in the 6-day window ending on ovulation day, which usually falls about 14 days before your next period. With a 28-day cycle that started on 1 October, ovulation would be around 15 October and the fertile window 10–15 October. Cycles vary, so use this as a guide.
- Ovulation ≈ next period − 14 days
- Fertile window: 5 days before ovulation + ovulation day
- Test for pregnancy from the day of your missed period
How does the ovulation calculator work?
Ovulation usually happens about 14 days before your next period starts. The calculator adds your cycle length to the first day of your last period to estimate your next period, then counts back 14 days to find your likely ovulation day.
Your fertile window is the 6 days ending on ovulation day, because sperm can survive for up to 5 days and the egg for about a day. With a 28-day cycle starting on 1 October, ovulation falls around 15 October and the fertile window runs from 10 to 15 October.
The estimate works best for regular cycles. If your cycles vary by more than a few days, ovulation tests or tracking your temperature give a better picture. This is not a method of contraception.
Frequently asked questions
How do I calculate my ovulation date?
Ovulation usually happens about 14 days before your next period. With a 28-day cycle that is around day 14; with a 32-day cycle, around day 18. Enter the first day of your last period and your cycle length above.
What is the fertile window?
The fertile window is the 5 days before ovulation plus the day of ovulation, because sperm can survive up to 5 days. The 2–3 days just before ovulation give the highest chance of pregnancy.
How accurate is an ovulation calculator?
It’s an estimate for regular cycles. Research shows many women ovulate on different days from cycle to cycle, so ovulation test kits or basal body temperature tracking give a more precise answer.
When should I take a pregnancy test?
Most home pregnancy tests are reliable from the first day of a missed period, about 14 days after ovulation.
What cycle length should I enter?
Count the days from the first day of one period to the first day of the next, and use the average of your last few cycles. The calculator accepts cycles from 21 to 45 days; 28 days is a common default.
Can I use the ovulation calculator if my periods are irregular?
You can, but the dates will be less reliable because it assumes every cycle is the same length. Try entering your shortest and longest recent cycles to see the earliest and latest likely dates, and talk to a doctor if your cycles vary a lot.