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Ovulation Calculator: Fertile Days and Next Period

ওভুলেশন ক্যালকুলেটর: উর্বর সময় ও পরের মাসিক

From the first day of your last period and your cycle length, see the days you are likely to ovulate and your next three period dates.

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Days from the first day of one period to the first day of the next. 28 if you’re not sure.

Nothing you enter is saved or sent anywhere, and this calculator keeps no history.

Your dates will appear here

Enter the first day of your last period, then select Show my dates.

How the ovulation days are worked out

  1. Next period = first day of the last period + cycle length.
  2. Likely ovulation = from 16 days to 10 days before the next period. The NHS says most women ovulate around 10 to 16 days before their next period, so we show that range rather than one exact day.

Example

Last period on 20 October 2026, 28-day cycle. The next period is 20 October + 28 days = 17 November. Likely ovulation is 16 to 10 days before 17 November: 1 to 7 November (days 13 to 19 of the cycle, around day 14). In the cycle after that it is 29 November to 5 December, with the next period on 15 December.

Fertile days and their limits

  • Sperm can survive up to 7 days, so sex in the days before ovulation can also lead to pregnancy.
  • If you are trying for a baby, the NHS suggests sex every 2 to 3 days rather than aiming for one day.
  • The NHS says cycles of 21 to 35 days are normal. Outside that, or with irregular cycles, the dates are less reliable.
  • This is not contraception: ovulation can come earlier or later. For a reliable method, ask a doctor or family planning service.

If you are pregnant, the Pregnancy Due Date Calculator gives your due date and how many weeks you are; to count days between dates, use the Date Difference Calculator.

How to use the calculator

  1. Enter the first day of your last period.
  2. Enter your cycle length in days (leave 28 if you’re not sure).
  3. Select Show my dates to see the likely ovulation days, today’s cycle day and your next three period dates.

The dates you enter are never sent anywhere, and for privacy no list of calculations is kept.

Sources

Checked on 2 November 2026. This is not medical advice.

Frequently asked questions

When do I ovulate?

The NHS says ovulation happens around 10 to 16 days before the next period in most women. With a 28-day cycle that is days 13 to 19, around day 14. With a 20 October period and a 28-day cycle, the likely days are 1 to 7 November.

When am I most likely to get pregnant?

Around ovulation. Sperm can survive up to 7 days, so sex in the days before ovulation can also lead to pregnancy. The NHS suggests sex every 2 to 3 days if you are trying for a baby, rather than aiming for one day.

How is my next period date worked out?

First day of your last period + your cycle length. A period on 20 October with a 28-day cycle means the next is due on 17 November.

What cycle length is normal?

The NHS says cycles of 21 to 35 days are normal. If yours is outside that, or changes a lot from month to month, the dates here are less reliable; talk to a doctor if your periods are very irregular.

Can I use this as contraception?

No. Ovulation can come earlier or later than expected, and this is only an estimate from dates. Use a reliable method of contraception and ask a doctor or family planning service.

Is what I enter saved?

No. The dates stay on your phone or computer and are never sent anywhere, and this calculator keeps no list of recent calculations.

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