Estimate the next three period start dates from the first day of the last period and a typical cycle length.
Calculate your estimate
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How this calculator can help
This can help with everyday planning and cycle logging. Cycles naturally vary, so each date is an estimate. The tool deliberately does not predict ovulation or a fertile window and must not be used for contraception.
How the estimate works
A menstrual cycle is counted from the first day of one period to the first day of the next. The calculator repeatedly adds the cycle length you provide. The Office on Women’s Health notes that regular adult cycles are often 24 to 38 days.
Sources and methodology
We use transparent formulas and primary public-health or research sources. Calculators simplify real life, so their results should be interpreted as estimates.