Calculator tool
The menstrual cycle averages 28 days but can range from 21 to 35 days. This calculator predicts upcoming period dates by adding your cycle length repeatedly from your last period start.
Review the inputs carefully and treat the output as an estimate. For decisions involving money, taxes, health, law, or security, compare the result with trusted professional guidance when needed.
What is a normal cycle length?
A normal menstrual cycle ranges from 21 to 35 days, with 28 days being average. Cycles shorter than 21 or longer than 35 days may warrant medical evaluation.
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Estimate your ovulation date and 6-day fertile window based on your last period and average cycle length.
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Estimate when conception likely occurred from an estimated due date, last menstrual period, or ultrasound dating.
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Calculate an estimated due date from LMP, conception date, ultrasound gestational age, or IVF embryo transfer.
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