Question 1

How do I calculate when my next period is due?

Accepted Answer

Count the number of days in your menstrual cycle (from the first day of one period to the first day of the next), then add that number to the first day of your last period. For example, if your last period started on June 1 and your cycle is 28 days, your next period is due around June 29. Our calculator above does this automatically and shows your next 6 cycles.

Question 2

Is a 28-day cycle normal?

Accepted Answer

Yes, 28 days is often cited as the average, but a normal menstrual cycle can range from 21 to 35 days in adults. What matters most is that your cycle is relatively consistent for you. A variation of a few days from month to month is completely normal.

Question 3

How accurate is a period calculator?

Accepted Answer

A period calculator is most accurate if your cycles are regular and you track at least 3–6 months of data. It predicts future periods based on your average cycle length, so stress, illness, travel, weight changes, and conditions like PCOS can shift your actual dates. Treat the prediction as an estimate with a margin of a few days, not a guarantee.

Question 4

What counts as the first day of my period?

Accepted Answer

Day 1 of your cycle is the first day of full menstrual flow — not light spotting. If you notice spotting a day or two before your period properly begins, that still belongs to your previous cycle. Tracking from full flow gives the most accurate cycle-length calculation.

Question 5

Why is my period late?

Accepted Answer

Common reasons for a late period include stress, significant weight change, excessive exercise, travel across time zones, illness, thyroid issues, polycystic ovary syndrome (PCOS), perimenopause, and pregnancy. If your period is more than a week late and pregnancy is possible, take a pregnancy test. Persistent irregularity warrants a visit to your doctor.

Question 6

Is it normal to get my period twice in one month?

Accepted Answer

It can be. If your cycle is naturally short (for example, 24 days), you may occasionally have two periods in one calendar month — one at the start and one at the end. However, bleeding twice a month regularly, or bleeding between periods, should be checked by a healthcare provider.

Question 7

How many days does a normal period last?

Accepted Answer

A typical period lasts between 3 and 7 days. Bleeding that consistently lasts longer than 7 days, is very heavy (soaking through a pad or tampon every hour for several hours), or comes with severe pain should be discussed with a doctor.

Question 8

Can I use a period calculator if my cycles are irregular?

Accepted Answer

You can, but predictions will be less reliable. With irregular cycles, use your average cycle length from at least 6 months of tracking, and expect a wider margin of error. If your cycles are consistently shorter than 21 days, longer than 35 days, or vary by more than 7–9 days month to month, it is worth discussing with a healthcare provider.

Question 9

When am I ovulating in my cycle?

Accepted Answer

Ovulation typically occurs about 14 days before your next period starts — not necessarily 14 days after your last one. In a 28-day cycle that is around day 14; in a 32-day cycle, around day 18. Your fertile window covers the 5 days before ovulation plus ovulation day itself. Use our ovulation calculator for a personalized estimate.

Question 10

Can a period calculator tell me if I am pregnant?

Accepted Answer

No. A period calculator can tell you when your period is due, and a missed period is often the first sign of pregnancy — but only a pregnancy test can confirm it. If your period is more than a few days late, take a home pregnancy test and consult your doctor if needed.

Question 11

When should I see a doctor about my periods?

Accepted Answer

See a doctor if your periods suddenly become irregular after being regular; you go 90 or more days without a period and are not pregnant; bleeding lasts more than 7 days; you bleed between periods or after sex; periods are accompanied by severe pain; or you are soaking through a pad or tampon every hour for 2 or more hours.

Question 12

Does this calculator store my data?

Accepted Answer

No. All calculations happen in your browser — your period dates never leave your device and are never sent to our servers. Unlike period-tracking apps, we do not collect, store, or share your personal health data.

Free Period Calculator – Track Your Next Cycle

How the period calculator works

Enter the first day of your last period

Set your average cycle length

See six estimated cycles

Understand your cycle

How cycle length is counted

Why predictions can shift

Frequently asked questions