Track and predict your next period, ovulation date, and fertile window from your cycle history. Free period calculator and tracker with a full cycle calendar.
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.
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.
Is this the same as a period tracker?
Yes. A period tracker and a period calculator both predict upcoming period and ovulation dates from your cycle history. This tool works as a quick, no-signup period tracker: enter your last period date, period length, and cycle length to see your current and upcoming cycles.
What counts as a late period, and how do I calculate it?
A period is usually considered late if it has not started within about 5 to 7 days after your estimated next period date from this calculator. Occasional lateness is common and can be caused by stress, illness, travel, or hormonal changes; a pattern of repeated lateness is worth discussing with a healthcare professional.
Can I use this calculator if my periods are irregular?
Yes, but treat the result as a rougher estimate. Enter your most typical cycle length as the average. With irregular cycles, the predicted next period and ovulation dates are less reliable than with a regular cycle, since the calculation assumes a consistent cycle length each month.
