Knowledge base
How reliable is a period prediction?
A prediction is an estimate based on your own cycles. The more you log, the narrower the margin gets, but it never reaches zero.
Where the number comes from
An app works from your recent cycles and weighs the latest ones more heavily. With one logged cycle the uncertainty is wide; after six months it is smaller. That difference should be visible, not polished away.
Why a margin is more honest
In a 28-day cycle, research found ovulation spread across ten days. An app showing a single date is hiding something it knows. Mensis shows a margin and says how wide it is.
What it is not
Fertile days are not contraception. A cycle app is not a medical device and cannot establish whether you are pregnant, whether it is safe, or whether something is wrong.
Sources
- Soumpasis, Grace, Johnson, Human Reproduction Open (2020), Real-life insights on menstrual cycles and ovulation using big data
- NHS, Periods and fertility in the menstrual cycle
General information, not medical advice. In doubt, or things are not going well? Call your doctor.
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