Period Calculator and Cycle Calendar

Written byOleh Soloninupdated 25 September 2026

First day of the last period

Cycle length, days

From the first day of one period to the first day of the next. If it varies, take the average over a few months.

Days of bleeding

Advanced options

Work out for

For example, to see whether a period falls during a holiday.

Result

Next period2026-10-24 (Saturday), in 18 days
Likely to end2026-10-28
Todayday 11 of a 28-day cycle
Possible ovulationaround 2026-10-08 to 2026-10-14
The three after that2026-11-21, 2026-12-19, 2027-01-16
Three-month calendar
October 2026 Mo Tu We Th Fr Sa Su 1 2 3 4 5 [ 6] 7 8 o 9 o 10 o 11 o 12 o 13 o 14 o 15 16 17 18 19 20 21 22 23 24 p 25 p 26 p 27 p 28 p 29 30 31 November 2026 Mo Tu We Th Fr Sa Su 1 2 3 4 5 o 6 o 7 o 8 o 9 o 10 o 11 o 12 13 14 15 16 17 18 19 20 21 p 22 p 23 p 24 p 25 p 26 27 28 29 30 December 2026 Mo Tu We Th Fr Sa Su 1 2 3 o 4 o 5 o 6 o 7 o 8 o 9 o 10 11 12 13 14 15 16 17 18 19 p 20 p 21 p 22 p 23 p 24 25 26 27 28 29 30 31 o [ ] today, p period, o possible ovulation

This result is informational only and is not professional advice.

Dates are worked out from today

When your next period is due, which day of the cycle you are on, and a three-month calendar marking period days and possible ovulation, from the first day of your last period and your cycle length.

The calculator adds your cycle length to the first day of your last period and shows the nearest dates after today, with period days and possible ovulation marked on a three-month calendar.

The average cycle is about 28 days, and regular cycles from 21 to 35 days are normal; periods usually last 2 to 7 days (NHS). The calculation assumes every cycle is the same length, so if yours varies, the real dates will shift.

How to use

Enter the first day of your last period.
Enter your cycle length, from the first day of one period to the first day of the next, and how many days your period usually lasts.
Read the next period date, today's cycle day and the three-month calendar. To check another date, such as a holiday, set it under "Work out for".

How the next period date is worked out

The first day of bleeding is day 1 of the cycle. Add the cycle length and you have the first day of the next period. If your last period was a while ago, the calculator adds cycles until it passes today and reminds you that the most recent period gives a closer estimate.

Today's cycle day is counted the same way: the day bleeding started is day 1. When the cycle day equals the cycle length, the next period is due tomorrow.

For a last period starting on 1 September 2026. Worked out with this calculator.
Cycle length	Next period	Possible ovulation	Then
26 days	27.09.2026	11.09 to 17.09	23.10, 18.11, 14.12
28 days	29.09.2026	13.09 to 19.09	27.10, 24.11, 22.12
30 days	01.10.2026	15.09 to 21.09	31.10, 30.11, 30.12
32 days	03.10.2026	17.09 to 23.09	04.11, 06.12, 07.01

When ovulation may happen

In most women ovulation, the release of an egg, happens around 10 to 16 days before the next period (NHS). That is why the calculator marks seven days rather than one. In a 28-day cycle that is days 13 to 19.

The longer the cycle, the later ovulation falls: in a 32-day cycle it comes four days later than in a 28-day one, because the calculator counts back from the next period. For timing conception, use the ovulation calculator.

What this calculator shows

The next period date, its weekday and how many days away it is
Roughly when it will end
Which day of the cycle today is
Possible ovulation days, 10 to 16 days before the period
Three more cycle dates and a three-month calendar

What to keep in mind

Every cycle is taken to be the same length. If yours vary, use the average of a few months; the dates will still be approximate.
The calendar does not tell you whether pregnancy is possible on a given day and is no substitute for seeing a doctor.

Where the numbers come from

Checked against NHS, "Periods and fertility in the menstrual cycle" (cycle length, period length, ovulation 10 to 16 days before a period) · verified September 2026.

FAQs

How do I work out when my next period is due?

Add your cycle length to the first day of your last period. If it started on 1 September and your cycle is 28 days, the next one is due on 29 September.

How do I know which cycle day I am on?

Count the days from the first day of your last period, counting that day as day 1. On 10 September, after a period that started on 1 September, you are on day 10.

What cycle length is normal?

About 28 days on average; regular cycles from 21 to 35 days are normal (NHS). If yours is regularly outside that range or changes a lot, talk to a doctor.

How many days does a period last?

Usually 2 to 7 days (NHS). Enter your own length: it sets the marks on the calendar and the date the period is likely to end.

When is ovulation in a 28-day cycle?

Around 10 to 16 days before the next period, which is days 13 to 19 of the cycle. A calendar cannot pin down the exact day.

Why didn't my period come on the calculated day?

The calculator treats every cycle as the same length, and in real life they differ. If a period is very late or it keeps happening, see a doctor.

Worked example

A 28-day cycle

Input: Last period 01.09.2026, 28-day cycle, 5 days of bleeding, worked out for 10.09.2026

Output: Next period 29.09.2026, ending around 03.10.2026

Note: Today is cycle day 10. Possible ovulation falls between 13 and 19 September, and the following periods are due on 27 October, 24 November and 22 December.

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Result

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