When did your last period start?
If you’re not sure, choose your best estimate.
How long is your average cycle?
Count the days from the first day of one period to the first day of the next. If you’re not sure, use 28 days as a starting point.
Go back to earlier months and pick 2–5 more period start dates. We’ll use the median and range of the gaps between them.
How many days does your period usually last?
If you’re not sure, use 5 days as a starting point.
Next expected period
Check for trip overlap
This range is a rough guide based on your recent cycles. If your cycles are irregular, the actual dates may differ.
With Kiyo
Your month — plans and your cycle, together on one calendar.
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How your next period is calculated
We estimate your next period by adding your average cycle length to the first day of your last period. The highlighted period dates reflect how long your period usually lasts.
This is an estimate. Your actual dates may vary from cycle to cycle.
Don’t know your average cycle length? You can use the start dates of your last 3 to 6 periods instead. The calculator takes the median gap between those dates to estimate your next period, then marks your next three expected start dates on the calendar, each with a range based on your shortest and longest recent cycles. It isn’t a tool for determining when you ovulate or when you’re fertile — it’s for checking ahead whether a trip or an important event might overlap your period.
Want more than the date? See how cycle planning works →Frequently asked questions
Can I use this calculator if my cycles are irregular?
You can, but the estimate may be less reliable if your cycle length varies. Once you’ve logged a few periods in Kiyo — enough to measure three full cycles — the app uses the median of your recent cycle lengths to estimate your next period. This reduces the influence of unusually short or long cycles. If you’re concerned about irregular periods, talk with a healthcare professional.
What if my period hasn’t started by the expected date?
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 my cycle information saved?
It stays in your browser while you use this calculator — nothing you enter is saved or sent anywhere.
If you select “Plan with Kiyo,” your entries are passed to the Kiyo calendar to display your cycle. They’re saved in the app only after you review and agree to the cycle data notice.
Do I need separate calendars for my period and my plans?
Kiyo brings both together. Your cycle dates are shown with subtle background colors alongside your events and to-dos, so you can see where your next period falls when you’re planning a trip or an important appointment. Cycle tracking is optional and off by default.
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.