Period Calculator
Are you on your period right now?
Knowing where you are right now makes todayโs position more accurate.
When did your last period start?
It does not have to be exact. Pick the day you remember.
How long is your average cycle?
That is the number of days from the first day of one period to the day before the next one starts. If you are not sure, leave it at 28.
How many days does your period usually last?
If you are not sure, leave it at 5.
How your next period is calculated
Your next expected period is calculated as the first day of your last period plus your average cycle length. The expected period itself runs from that date for as many days as your period usually lasts.
Because it works from an average, the result can drift from what actually happens when cycles vary. Logging the start date each month lets the calculation run on the average of your own records, so the estimate moves closer to you over time. In Kiyo, once records build up, it uses the median of your recent cycles, so a single month that lands far off does not throw the whole estimate.
Frequently asked questions
How do I calculate this if my cycles are irregular?
A simple calculator leans on a single average, so it does not fit variable cycles well. That is all the more reason to log your start date every month. Once records build up, the calculation can use the median of your recent cycles, so one month that lands far off moves the estimate less. If your cycles remain very irregular, consider talking with a healthcare professional.
My expected date has passed and my period has not started.
An expected date comes from an average, so being off by a few days is common. Once you know the actual start date, run the calculation again from that day. If the situation worries you, talk with a healthcare professional.
Can I use this calculator for birth control?
No. Do not use this calculator as a method of birth control.
Is the date I enter saved anywhere?
No. Everything on this page is calculated inside your browser, and what you enter is neither saved nor sent to a server. Even when you start recording cycles in the Kiyo app, records are stored only after you give separate consent.
Do I need a period calendar and a regular calendar?
In Kiyo they are one calendar. The cycle you record is laid underneath in a light tint, with your schedules and to-dos on top of it. When you are booking a trip or an important appointment, you can see where your next period falls first. Cycle tracking is optional and off by default, so you can turn it on only if you want it.
โป This calculator and its cycle information are for general reference only and are not intended for medical diagnosis or treatment. Cycles vary from person to person. Do not use this calculator for birth control. If you have severe pain, persistent irregular bleeding, or other health concerns, talk with a qualified healthcare professional.