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Pregnancy Due Date Calculator

Estimate your due date from your last period or conception date, see how far along you are right now, and which trimester you're in — no account, nothing stored.

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Last period start date

Conception date

First day of your last period

Estimated Due Date

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Enter a date above to calculate

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Weeks pregnant

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Trimester

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Days to go

Conception40 weeks

Trimester timeline

Trimester	Weeks	Date range

Pregnancy is typically counted as 40 weeks from the first day of your last period — about 2 weeks before conception actually happens. This is the standard medical convention, not an error.

This is an estimate, not a diagnosis. Only about 5% of babies are born on their exact due date — most arrive within 2 weeks before or after. Your OB/midwife will refine this estimate using an early ultrasound, which is generally more accurate than date-based calculations alone. Always follow your healthcare provider's guidance over this tool.

Quick answers

How accurate is the last-period method?

It assumes a textbook 28-day cycle with ovulation on day 14 — the same assumption used in the standard "Naegele's Rule" formula (due date = last period start + 280 days). If your cycles are longer or shorter than 28 days, your actual due date may shift by several days in either direction. An early ultrasound (typically 8–12 weeks) gives a more precise estimate.

Why 40 weeks if conception happens around week 2?

Medical convention counts pregnancy from the last menstrual period rather than the conception date, mostly because the LMP date is something people usually know for certain, while the exact conception date often isn't. So "40 weeks pregnant" really means about 38 weeks since conception.

What happens after my due date passes?

Most pregnancies that go past the due date are still perfectly normal — babies born anywhere from 37 to 42 weeks are considered full-term or later. Your provider will typically monitor more closely if you go past 40–41 weeks and discuss options like induction if needed. This is a conversation for your provider, not something to self-manage from a due date estimate.