How is the due date calculated?

It uses Naegele's rule: 280 days (40 weeks) from the first day of your last menstrual period, adjusted for cycle lengths longer or shorter than 28 days.

Is this calculator medically accurate?

It provides an estimate only and is not medical advice. Only about 4 percent of babies arrive on the exact due date. Always confirm dating with your healthcare provider, who may use an ultrasound for greater accuracy.

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Pregnancy Due Date Calculator

Estimate a due date from the last period.

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How to use the Pregnancy Due Date Calculator

1Enter the first day of your last menstrual period (LMP).
2Adjust your average cycle length if it differs from 28 days.
3View your estimated due date, current week, and trimester.

About the Pregnancy Due Date Calculator

Free pregnancy due date calculator: enter your last menstrual period and cycle length to estimate your due date, current week of pregnancy, and trimester.

Part of our Calculators collection. Browse all tools.

Frequently asked questions

How is the due date calculated?: It uses Naegele's rule: 280 days (40 weeks) from the first day of your last menstrual period, adjusted for cycle lengths longer or shorter than 28 days.
Is this calculator medically accurate?: It provides an estimate only and is not medical advice. Only about 4 percent of babies arrive on the exact due date. Always confirm dating with your healthcare provider, who may use an ultrasound for greater accuracy.