Period Calculator | Next Period, Ovulation, Fertile Window

Q: What does a period calculator estimate?

A period calculator estimates your next period date , expected period days , ovulation date , and fertile window from your last period date, period length, and average cycle length.

Q: How is the next period date calculated?

It is estimated as the first day of your last period + average cycle length . If your cycle is fairly regular, this gives a practical estimate of when the next period may begin.

Q: How is ovulation estimated in this calculator?

Ovulation is estimated at about 14 days before the next period . That is a common cycle-tracking rule of thumb, but real ovulation can happen earlier or later.

Q: What is the fertile window?

The fertile window is usually the 5 days before ovulation plus the day of ovulation . This is the part of the cycle when pregnancy is most likely.

Period calculator to estimate your next period, period days, ovulation date, fertile window, and upcoming cycles from your last period date, period length, and cycle length.

Use this period calculator to estimate your next period date, period days, ovulation date, and fertile window from the first day of your last period, your usual bleeding length, and your average cycle length.

It also lays out several upcoming cycles in table and calendar form, which makes it useful for general cycle tracking, planning ahead, and understanding when your next period or ovulation is most likely. The results are estimates only and can vary from month to month.

First day of your last menstrual period

day	month	year

How long did it last?

days

Number of days in your cycle

days

Current cycle estimate

Estimated period days: -
Estimated ovulation date: -
Most fertile days: -
Fertile window: -
Estimated next period date: -

Upcoming cycle estimates

Cycle	Period	Ovulation	Fertile window	Next period

Estimated period calendar

Period days Fertile window Ovulation

This calculator gives cycle estimates only and is not a medical tool. Period timing, bleeding length, and ovulation can vary from cycle to cycle.

Period Calculator FAQ

What does a period calculator estimate?
A period calculator estimates your next period date, expected period days, ovulation date, and fertile window from your last period date, period length, and average cycle length.

How is the next period date calculated?
It is estimated as the first day of your last period + average cycle length. If your cycle is fairly regular, this gives a practical estimate of when the next period may begin.

How is ovulation estimated in this calculator?
Ovulation is estimated at about 14 days before the next period. That is a common cycle-tracking rule of thumb, but real ovulation can happen earlier or later.

What is the fertile window?
The fertile window is usually the 5 days before ovulation plus the day of ovulation. This is the part of the cycle when pregnancy is most likely.

Can I use this as a medical or birth control tool?
No. This calculator provides estimates only and should not replace medical advice, cycle-specific fertility testing, or contraception guidance. Stress, illness, hormone changes, travel, and irregular cycles can all shift timing.

How many future cycles can this help me plan?
This version shows your current cycle estimate, a table of upcoming cycles, and a compact calendar view so you can see likely period days and ovulation timing at a glance.