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Due Date Calculator

Estimate your due date three ways — from your last period, a known conception date, or an ultrasound scan — and see the week-by-week timeline that comes with it.

A due date is a best estimate, not a deadline: only around 5% of babies arrive on the day itself. Pick the method that matches what you know, and this page works out the rest — current week, trimester dates and the typical screening windows ahead.

Free, no sign-upRuns 100% in your browserNaegele's rule + cycle adjustment
The first day, not the last day, of your most recent period.
28 is the standard assumption. Longer or shorter cycles shift the estimate.

Your estimated due date is

Method
You are (today)
Trimester
Estimated conception
First trimester ends
Second trimester ends

Your timeline ahead

    Please read: This calculator gives estimates only — it is not medical advice and cannot diagnose or date a pregnancy with certainty. Only around 5% of babies arrive on their estimated due date, and most arrive within a week or so either side. Ultrasound dating performed by a clinician takes precedence over any calculator result. Always confirm your dates, screening windows and care plan with your healthcare provider. All dates are processed locally in your browser; nothing you enter is uploaded or stored.

    Three ways to estimate a due date

    Last period (Naegele's rule)

    The classic method: 280 days from the first day of your last period, adjusted if your cycle is not 28 days. Simple and standard — but it assumes you ovulated on day 14.

    Conception date

    If you know when conception likely happened, add 266 days. Often the best option after ovulation tracking or fertility treatment.

    Ultrasound

    An early scan measures the embryo directly. Providers often treat a first-trimester ultrasound as the most reliable dating method, and it can override the other two.

    Related calculators

    Ovulation CalculatorFind your likely ovulation day and fertile window from your cycle. How Many Weeks Pregnant Am I?Turn any date into weeks + days and a trimester. Pregnancy Timeline, Week by WeekWhat typically happens from week 1 to week 40. Conception CalculatorWork from a conception date — or backwards from a due date. Due Date by UltrasoundReproduce the scan-based estimate step by step. How Due Dates Are CalculatedNaegele's rule, the 266-day method and why dates move.

    Frequently asked questions

    How is my due date calculated from my last period?

    The standard method is Naegele's rule: take the first day of your last menstrual period (LMP), add 280 days (40 weeks). If your cycle is usually longer or shorter than 28 days, this calculator adjusts by the difference — a 32-day cycle adds 4 days, for example.

    How accurate is a due date calculator?

    It is an estimate. Only around 5% of babies are born on their estimated due date, and most arrive within roughly a week either side. An ultrasound measurement in the first trimester is generally considered more precise, and your clinician's dating takes precedence.

    What if I know my conception date instead?

    Use the Conception tab. Pregnancy is typically counted as 266 days (38 weeks) from conception to the estimated due date, because the standard 280-day count assumes conception happens around day 14 of the cycle.

    Can an ultrasound change my due date?

    Yes. If an early ultrasound measurement suggests a meaningfully different gestational age than the LMP-based estimate, your provider may revise the due date. The ultrasound tab on this page lets you reproduce that style of calculation.

    What does 'gestational age' mean?

    Gestational age is how far along a pregnancy is measured from the first day of the last period — so it is about two weeks more than the time since conception. It is usually written as weeks plus days, such as 12 weeks, 3 days.

    Is my data private?

    Yes. Every calculation runs in your browser. The dates you enter are never sent to a server, stored, or shared.