Ovulation Calculator – Find Your Fertile Days and Ovulation Date

Ovulation is when an ovary releases an egg. In most cycles it happens about 14 days before the next period starts. The egg lives for about a day, but sperm can survive in the body for up to 5 days, so the chance of pregnancy is highest in the fertile window: the 5 days before ovulation and the day of ovulation itself.

This calculator uses your last period and cycle length to estimate these days.

How to use the ovulation calculator

Enter the first day of your last period (the first day of bleeding is day 1).
Enter your usual cycle length: the number of days from the first day of one period to the first day of the next. 28 days is common, but anything from 21 to 35 days is normal.

You will see your next fertile window, likely ovulation day, next period date and which day of your cycle it is today. Open the table below the result for your next 6 cycles.

How it is calculated

Ovulation day  = First day of last period + (cycle length − 14 days)
Fertile window = 5 days before ovulation to the ovulation day
Next period    = First day of last period + cycle length

Example

Your last period started on 1 October 2026 and your cycle is 28 days.

Ovulation: 1 October + 14 days = Thursday, 15 October 2026
Fertile window: 10 – 15 October
Next period expected: 29 October 2026

With a 32-day cycle, ovulation would be around 19 October, the fertile window 14 – 19 October, and the next period around 2 November.

How to know more exactly

A calendar estimate works best for regular cycles. These signs help you confirm ovulation:

Ovulation test kits (LH strips) from a chemist turn positive 1 to 2 days before ovulation.
Cervical mucus becomes clear, slippery and stretchy, like raw egg white, around the fertile days.
Basal body temperature, measured each morning before getting up, rises slightly after ovulation.

Important

Cycles can shift with stress, illness, travel, weight change or conditions such as PCOS or thyroid problems.
This is not a method of birth control. Counting days alone often fails. Talk to a doctor about contraception.
A home pregnancy test is most reliable from the day your period is due.

FAQ

Can I get pregnant outside the fertile window?

It is less likely but possible, because ovulation doesn't always happen on the same day. That is also why calendar counting is not reliable for avoiding pregnancy.

What if my periods are irregular?

The calculator will be less accurate. Track your cycles for a few months, use ovulation test kits, and see a doctor if your cycles are often shorter than 21 days or longer than 35 days.

How long should we try before seeing a doctor?

Doctors usually suggest seeing a specialist after 12 months of regular unprotected sex without pregnancy if the woman is under 35, and after 6 months if she is 35 or older. See one sooner if periods are very irregular or you have a known health issue.

I think I am pregnant. What next?

Take a home pregnancy test on or after the day your period is due, and visit a doctor. You can estimate your delivery date with the pregnancy due date calculator.