Period Calculator: Next Period Date & Cycle Forecast
See your next period and the six after it.
Cycle Length Calculator: Average Cycle & Regularity Check
Average several cycles and see how regular you are.
⟨/⟩ Embed this tool on your site
Paste this into any page — the live tool appears with a credit link back here.
✏️ Sketching your tool…
Sponsored: Recommended offer →
About Cycle Length Calculator: Average Cycle & Regularity Check
Enter each recent period start date to get your average cycle length, shortest and longest cycle, and a regular or irregular verdict.
How is average cycle length measured?
Each cycle length is the number of days between the start of one period and the start of the next. The calculator averages every usable gap and reports the shortest and longest cycle so you can see the spread, not just the mean.
Why are some gaps ignored?
Gaps under 15 days are physiologically impossible and are treated as typos. Gaps over 60 days usually mean a period was missed and the date was not recorded, so counting it would drag your average down. Both are flagged in the results table.
📐 Methodology & Reference Accuracy:
Calculations, formulas, and conversions execute locally in your web browser. Output models are benchmarked against official reference standards and updated for 2026.
🔒 This tool runs entirely in your browser. Nothing is uploaded or stored.
Background reading: Cycle Length Calculator on Wikipedia. More: all women's health.
Frequently Asked Questions about Cycle Length Calculator: Average Cycle & Regularity Check
What counts as a regular cycle?
A cycle varying by 7 days or less across your tracked periods is generally considered regular. Variation up to about 14 days is common and often normal. Larger swings are worth discussing with a clinician if they repeat.
How many periods do I need to enter?
Two dates are enough to produce a result, but six or more tracked periods give a much more stable average and a fairer regularity verdict.
What if my periods are irregular?
Enter every date you have anyway: the calculator still reports your average, shortest and longest cycle, and flags the verdict as irregular. Use the shortest cycle for conservative planning, such as a period calculator forecast, and speak to a clinician if large swings repeat.