When is my next period due?
Add your average cycle length to the first day of your last period. If your cycle is 28 days and your last period started on 1 October, expect the next one around 29 October. Enter your own details below to see your next 6 periods.
Enter a date to calculate.
Everything is calculated on your own device. We store nothing and send nothing anywhere.
This is an estimate, not medical advice and not contraception. If in doubt, ask your GP or midwife.
How we calculate
Your cycle runs from the first day of one period to the day before the next. We add your average cycle length to the first day of your last period, and the length of your period gives the end date.
What is a normal cycle?
A cycle between 21 and 35 days is normal, and a period usually lasts 2 to 7 days. A few days of difference each month is normal too.
Why can it come out differently?
Stress, illness, travel, exercise, stopping the pill, breastfeeding and perimenopause can all shift your cycle. The more cycles you log, the better a prediction gets.
Want to know every month, without the maths?
PERIOD. learns from your own cycles and keeps your predictions up to date. Free, no ads, and we never sell your data.
Frequently asked questions
How do I calculate when my next period is due?
Add your average cycle length to the first day of your last period. With a 28 day cycle, your next period starts 28 days after the first day of the previous one.
How long is a normal cycle?
Between 21 and 35 days. A few days of difference each month is normal.
How accurate is a period calculator?
It is an estimate based on your average. If your cycle varies, your period can come a few days earlier or later. An app that learns from your own cycles gets more accurate the longer you log.
My period is late, what now?
If you could be pregnant, take a pregnancy test from the day your period was due. If your period stays away for longer and you are not pregnant, ask your GP.
Read more
Other free tools
Sources: NHS, Periods and fertility in the menstrual cycle; NHS, Pregnancy due date; ACOG, Methods for estimating the due date.