Is this as accurate as my doctor's estimate?

An early ultrasound is generally considered more accurate than date-based methods alone, especially for irregular cycles — use this as a rough guide and confirm with your provider.

What if I don't know my last period date?

Your OB/GYN can estimate gestational age using an ultrasound instead, which doesn't rely on menstrual history.

Due Date Calculator

Estimate your pregnancy due date and current gestational age from your last menstrual period.

First day of last menstrual period

Average cycle length (days)

Estimated due date Choose your last period's start date

This is a general estimate (Naegele's rule, adjusted for cycle length). Your OB/GYN's ultrasound-based estimate is more accurate — always confirm dates and any health questions with your provider.

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How due dates are estimated

This calculator uses Naegele's rule: adding 280 days (40 weeks) to the first day of your last menstrual period, adjusted for cycle lengths other than 28 days. It's a widely used starting estimate, but only about 5% of babies arrive exactly on their calculated due date — most arrive within a couple of weeks of it.

Frequently asked questions

Is this as accurate as my doctor's estimate?: An early ultrasound is generally considered more accurate than date-based methods alone, especially for irregular cycles — use this as a rough guide and confirm with your provider.
What if I don't know my last period date?: Your OB/GYN can estimate gestational age using an ultrasound instead, which doesn't rely on menstrual history.