Next Period Calculator
Project your next several periods from cycle history — a paper calendar's worth of dates in one tap.
Cycles within ±4 days of personal average are normal variation — stress, illness, travel and big training weeks all shift ovulation, and the period follows ovulation by a fixed ~14 days. Projections drift as they extend; re-anchor on each real period. Consistently irregular or >38-day cycles deserve a clinician conversation.
Formula
For general information only. Pregnancy and infant care decisions must be guided by your treating clinician or midwife — always defer to their assessment.
Project your next several periods from cycle history — a paper calendar's worth of dates in one tap. The Next Period Calculator is a free, private next period calculator tool — every result computes instantly in your browser with no sign-up and no data upload.
About Next Period Calculator
Cycles within ±4 days of personal average are normal variation — stress, illness, travel and big training weeks all shift ovulation, and the period follows ovulation by a fixed ~14 days. It applies each period = LMP + n × average cycle length. Use the Next Period 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 Next Period Calculator
- 1Enter your details in the Next Period 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 Next Period Calculator?
- ✓Instant next period calculator 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 Digital Medicine 2019 — real-world cycle variability (600k cycles))
- ✓Free forever with no sign-up, account or app install
Frequently asked questions
How does the Next Period Calculator work?+
Cycles within ±4 days of personal average are normal variation — stress, illness, travel and big training weeks all shift ovulation, and the period follows ovulation by a fixed ~14 days. The calculation uses the formula: each period = LMP + n × average cycle length. Everything runs instantly in your browser as you type — your inputs are never uploaded.
Is the Next Period Calculator accurate, and what is it based on?+
The method is traceable to authoritative sources: Bull JR et al., npj Digital Medicine 2019 — real-world cycle variability (600k cycles). Results are estimates — individual variation always applies, so treat the output as a well-grounded starting point.
Is the Next Period 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 Next Period Calculator for?+
It's commonly used for next period calculator, period calendar, when is my next period. Project your next several periods from cycle history — a paper calendar's worth of dates in one tap.
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