A best guess, and how sure it is.

Splash estimates your next period and fertile window as a range, with confidence, using your own history. Irregular cycles welcome.

In short: Splash predicts your next period and fertile window from your last six cycles and shows each as a range, not a single date. Ranges tighten as you log more and widen honestly when cycles vary, including with irregular cycles or PCOS. Predictions are estimates, and Splash is not contraception.

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Insights: next period most likely Sat 21 Nov, anywhere from 19 to 23 Nov, with high confidence

Period and fertile-window estimates shown as honest ranges.

Ranges, not one magic date
Splash shows a most-likely day and a window around it, with how confident it is.
See how accurate it has been
Estimates use your own cycle history, not a textbook 28 days, and an accuracy card shows how close past guesses landed.
Long and irregular cycles
Cycles up to 90 days count, for PCOS and perimenopause. Wide ranges are shown honestly, and an early bleed asks “New period or spotting?” instead of restarting your cycle.
Not contraception
Fertile-window estimates are for awareness only. If you are avoiding pregnancy, use a method that is.

Why does Splash show ranges instead of one date?

Splash shows your next period as a most-likely day and a window around it, for example “Sat 21 Nov, anywhere from 20 to 22 Nov”. It also tells you how confident it is, based on how many cycles you have logged and how much they vary.

How does Splash predict my period?

New users start from a sensible default. After two or three logged periods, estimates are based on you. Logging ovulation tests or temperature can narrow the fertile-window estimate.

Ovulation, with a confidence label

The ovulation estimate is labelled Estimated, Likely or Confirmed, and shows how it was worked out. LH tests, mucus, temperature and PdG can all move it. With PCOS or irregular cycles, more than one LH rise stays possible until other signs agree.

How accurate has it been for me?

An accuracy card in Insights compares past estimates with when your periods really came, so you can see how much to lean on the next one.

New period or spotting?

If bleeding starts only a couple of weeks after your last period, Splash asks whether it is a new period or spotting, so a light bleed does not restart your cycle. Days that have not happened yet cannot be logged by mistake.

Why did my prediction change?

Stress, travel, illness and life stages all move cycles. When a period arrives early or late, Splash updates quietly. The calendar marks predicted days with dashed circles so a guess never looks like a fact.

Can I use predictions as contraception?

They are estimates, not contraception and not a diagnosis. If something changes a lot, the library explains when it is worth talking to a doctor.

Questions

How does Splash predict my period?

It looks at the cycles you have logged, works out a typical length and how much it varies, and shows a most-likely day with a window around it.

Why a range instead of a date?

Because cycles vary. A large 2019 study found only about 13% of cycles were exactly 28 days. A range is more honest than a single date.

Can I use the fertile window as contraception?

No. Splash is not contraception. If you are avoiding pregnancy, use a method that is.

What if my cycles are irregular?

Splash still works, with cycles up to 90 days counted for PCOS and perimenopause. The window will be wider, and it says so plainly instead of pretending to be sure.