Irregular Period Tracker

Predict a window for your next period when cycles vary. Free, private and instant.

How to use the Irregular Period Tracker

  1. Add one row per entry for period start dates: First day of period.
  2. Press Calculate to get an instant result with a colour scale, chart and plain-English explanation.

About the Irregular Period Tracker

If your cycles vary, a single date is not enough. This tracker uses your past periods to give a window in which your next period is likely to start, shows how irregular your cycles are and flags patterns worth discussing with a doctor.

Also known as: irregular period calculator, irregular cycle predictor, irregular period due date, period predictor for irregular cycles.

Formula and cut-offs

Window = last period start + shortest cycle to last period start + longest cycle. Variation = longest - shortest. Regular is 7 days or less; more than 9 days is irregular.

Frequently asked questions

What counts as an irregular period?

Cycles shorter than 21 days, longer than 35 days, or varying by more than 9 days from month to month.

What causes irregular periods?

PCOS, thyroid problems, stress, weight change, intense exercise, perimenopause and some medicines.

How can I predict ovulation with irregular cycles?

Use ovulation (LH) tests or track basal body temperature instead of a calendar.

Sources and references

Written and checked by the MediHub editorial team against the sources above. Read how we build and review our calculators.

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Last updated . This calculator is for education only and is not medical advice. See the medical disclaimer.