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How it works

From a few taps to a clear forecast

FlowKeeper turns the days you log into honest predictions — entirely on your device. Here's the whole journey, step by step.

Step 1

Log your days

Tap any day on the calendar to mark your period and record how you feel.

  • Flow — light, medium, or heavy
  • Symptoms, mood & energy — cramps, headache, and more
  • Pain level & notes — whatever you want to remember

Just a few logged cycles is enough for FlowKeeper to start predicting.

June 2026
MTWTFSS
8 9 10 1112 13 14 15 161718192021
Period Fertile Ovulation
Step 2

FlowKeeper learns your rhythm

Behind the scenes, a robust statistical model studies your history — built to handle real life, not a textbook.

Cleans the noise. Implausible or one-off cycles are filtered out before any math runs, so a single odd month doesn't skew your forecast.
Weighs the recent. Newer cycles count more than old ones, so the estimate tracks your body as it changes.
Measures certainty. The model also gauges how regular you are — and tells you, honestly, how confident the prediction is.
Recency weighting now −1 −2 −3

Each older cycle counts a little less than the one after it.

Step 3

Stay one step ahead

See what's coming — and choose to be reminded before it arrives.

  • Predicted period, ovulation & fertile window on your calendar
  • A clear high / medium / low confidence label on every estimate — tap it to see what it means
  • Optional reminders before your period or fertile window

All reminders are scheduled locally on your device — they never pass through a server.

High confidence

Next period

Mon, Jul 6

Likely to start: Jul 5 – Jul 7


OvulationJun 22
Fertile window opensJun 17
Go deeper

Curious about the actual math?

We've written the full, formula-by-formula explanation of how the next-cycle estimate is computed — with worked examples and graphs.

Read “Cycle Calculation”

Ready to try it?

Available on iPhone today. Coming to Android soon.

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