Period calculator

Add the first day of your last period and your usual cycle. You get the likely start of your next three, to help you plan ahead.

Your details

Your next period is likely to start

Thu 29 October 2026

give or take a few days

Lasting until about2 Nov
The one after26 Nov
And then24 Dec
Today is cycle day21

Stress, illness, travel and hormonal contraception all move periods. A few days early or late is normal.

Periods that are very heavy, very painful, come less than 21 or more than 40 days apart, or bleeding between periods or after sex: see your GP.

The working

Counting forward

Day 1 is the first day of bleeding. With a 28 day cycle and a period that started on 1 October, the next is due on 29 October, then 26 November and 24 December. A 32 day cycle moves each one 4 days later.

What is normal

Cycles vary

Thing	Usual range
Cycle length	21 to 40 days (NHS)
Average	28 days, but only some people are exactly 28
Period length	2 to 7 days
Variation, shortest to longest	7 days or less at 26 to 41, 9 days or less at 18 to 25 and 42 to 45 (FIGO)

If your cycles vary

Earliest and latest dates

Add your shortest and longest recent cycles and we show the window your next period could start in, and whether the spread counts as regular. Shortest 26 and longest 35 days from 1 October gives 27 October to 5 November. That 9 day spread is regular at 18 to 25 but more than the 7 days FIGO uses at 26 to 41. Varying cycles are common, so this is worth mentioning to your GP rather than worrying about.

Things that move a period

Not just pregnancy

Stress, illness or a big change in routine
Travel across time zones
Losing or gaining weight, or training hard
Starting or stopping hormonal contraception
Breastfeeding, and the years before the menopause

Read with care

What this cannot tell you

PregnancyA late period could be pregnancy; a test from the first missed day is reliable.
Irregular cyclesIf your cycle varies a lot, dates are a rough guide only.
ContraceptionNever use period dates as contraception.

Questions

Common questions

How do I work out my next period?

Add your cycle length to the first day of your last period.

Is a 35 day cycle normal?

Yes. The NHS says cycles from 21 to 40 days are normal.

Why is my period late?

Stress, illness, weight change and contraception are common reasons. If you could be pregnant, take a test.

Sources

Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.

Support when you need it

Contact your midwife or GP any time you are worried, and call NHS 111 if you cannot reach them. If a date or a result brings up difficult feelings, Tommy's and the Miscarriage Association offer kind, free support.