Next period calculator
Last period start + average cycle length ≈ next period start. No social feed, no fertility score gamification. Estimate only — not medical advice.
Enter a date to see an estimate.
What this page does
One-off arithmetic for trips and rough planning. If you are already pregnant, this page is the wrong tool.
We also show the following two estimated starts so you can sketch a quarter without installing a tracker.
When to use
Packing trips; rough planning; sanity-checking an app.
When not to
Contraception decisions. Wildly irregular cycles — show uncertainty; averages mislead.
Assumptions
Browser-only planning arithmetic. Defaults are disclosed on the page. Ultrasound and clinic policy override this tool.
Examples
LMP Jul 1, 2026 · cycle 28 → Next Jul 29, 2026.
LMP Jul 1, 2026 · cycle 32 → Next Aug 2, 2026.
Gotchas
Clinic dating after ultrasound can differ from browser math — the clinic wins for medical decisions.
Wrong input dates (retrieval vs transfer, spotting vs true LMP) slide every result.
Estimate only — not medical advice.
How this is calculated
The math stays in your browser. Enter the dates you actually know, read the estimate, and treat clinic ultrasound dating as the authority when it disagrees.
Nothing here is medical advice, a diagnosis, or a substitute for prenatal care.
- Enter the date(s) or numbers this page asks for.
- Check the assumptions under the result and on Methodology.
- Compare with your clinic portal if you have one.
- Use related tools if you only have a different kind of date.
- Confirm medical decisions with your clinician.
nextPeriod = LMP + cycleLength (also +2 and +3 cycles).
Related calculators
Synonym hub: period calculator. Full cycle stats: menstrual cycle calculator.
See also: period calculator, menstrual cycle calculator, and luteal phase calculator.
FAQ
- How do you predict the next period?
- Last start + average cycle length.
- What if my cycles vary?
- Use a range or recent shortest/longest cycles.
- Can stress delay a period?
- Yes — the calculator will not know.
- Is this Flo?
- No — one-off math, no account.
- Already pregnant?
- Use pregnancy dating tools instead.
- Is this medical advice?
- Estimate only — not medical advice. Confirm dating, testing, and medical decisions with your clinic.