Period Late Calculator
How late is late? Days overdue against your own variability, with the sane decision tree.
A period is only meaningfully 'late' relative to *your* spread — someone with 26–34-day cycles isn't late on day 31. Beyond pregnancy, the usual suspects that delay ovulation (and therefore the period that follows it by ~14 days) are stress, illness, travel, sudden training increases and weight change. Three or more absent months (amenorrhoea) is a clinician visit regardless of cause.
Formula
For general information only. Pregnancy and infant care decisions must be guided by your treating clinician or midwife — always defer to their assessment.
How late is late? Days overdue against your own variability, with the sane decision tree. The Period Late Calculator is a free, private period late tool — every result computes instantly in your browser with no sign-up and no data upload.
About Period Late Calculator
A period is only meaningfully 'late' relative to *your* spread — someone with 26–34-day cycles isn't late on day 31. It applies overdue days vs your personal cycle spread (not the textbook 28). Use the Period Late Calculator to get an instant, clearly-explained result with the working shown step by step — free, private and with the source method cited.
How to use Period Late Calculator
- 1Enter your details in the Period Late Calculator input fields above.
- 2The result updates instantly with the working and reference bands shown.
- 3Adjust any value to explore how it changes the outcome — it's free and unlimited.
Why use Period Late Calculator?
- ✓Instant period late result that recomputes as you type — no waiting, no page reloads
- ✓100% client-side: your health data never leaves your browser
- ✓Shows the actual formula and your numbers substituted in, so you can see exactly how the result is reached
- ✓Based on published, citable sources (Bull JR et al., npj Digit Med 2019 — cycle variability)
- ✓Free forever with no sign-up, account or app install
Frequently asked questions
How does the Period Late Calculator work?+
A period is only meaningfully 'late' relative to *your* spread — someone with 26–34-day cycles isn't late on day 31. The calculation uses the formula: overdue days vs your personal cycle spread (not the textbook 28). Everything runs instantly in your browser as you type — your inputs are never uploaded.
Is the Period Late Calculator accurate, and what is it based on?+
The method is traceable to authoritative sources: Bull JR et al., npj Digit Med 2019 — cycle variability. Results are estimates — individual variation always applies, so treat the output as a well-grounded starting point.
Is the Period Late Calculator free and private?+
Yes. It's completely free with no sign-up, and all computation happens locally in your browser, so none of your health data ever leaves your device.
Can I use this for medical decisions?+
This tool is informational only. Always defer to your treating clinician or midwife for pregnancy and infant care decisions.
What can I use the Period Late Calculator for?+
It's commonly used for period late, how late is my period, missed period calculator. How late is late?
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