When will my next period start?

HeySis works it out for you: tap the first day of your last period, and the home screen shows how many days are left. It's an estimate, and every cycle you log gives it more to go on.

How this works

Tap the first day of your last period, and HeySis fills in the rest of it.
The home screen counts the days left, and the calendar shows the forecast.
When your period starts, log day one, and the forecast updates.

How exact is the forecast?

At first the forecast window is about ±3 days. After a couple of cycles it can narrow to about a day, and if your cycle is irregular it stays wider. Until you have history, it uses the cycle length you entered, so bring your old dates in from calendar screenshots or Apple Health.

Will it remind me?

Yes, once you allow notifications. Mia, your AI sister in HeySis, writes a couple of days before your period, so the pads are already in your bag, and again on the morning it's due. Switch on “If your period is late”, and she'll also ask whether it has started. A home-screen widget shows the days left too.

The calendar, forecast, reminders and the whole diary are free, and Premium is optional.

Common questions

Does the period calendar work offline?

Yes. The diary, calendar and forecast work on your iPhone without internet.

My period is late. What should I do?

Stress, sleep or illness can shift a cycle. If pregnancy is possible, you can take a test from the first day your period is late.

What if my cycle is irregular?

Then the forecast window is wider, because your dates really do move around. Your cycle history in HeySis shows how long each cycle was, so you can see the spread yourself.

When will my next period start?

How this works

How exact is the forecast?

Will it remind me?

Common questions

More to read

Irregular cycle: is it normal?

Late period? Don't panic

Menstrual phase