Pregnancy Due Date Calculator
Estimate your due date from your last period, conception date — or reverse it from a due date.
The Due Date Calculator estimates when a baby is due and tracks the pregnancy week by week. Enter the first day of your last menstrual period (LMP) — the standard clinical starting point — or the conception date if you know it, and the tool returns the estimated due date, the current gestational age in weeks and days, the trimester, and the days remaining.
Pregnancy is conventionally dated from the LMP at 40 weeks (280 days), even though conception typically happens about two weeks later. This calculator follows that convention: due date = LMP + 280 days, with conception estimated around day 14 of your cycle (adjustable if your cycle differs from 28 days). If you already have a due date from an ultrasound, a third mode works backwards to show the LMP and conception dates implied by it.
Only about 4–5% of babies arrive exactly on their due date — providers treat it as a target window, not a promise, and dating scans can shift it by days. All figures are estimates for planning and education, calculated privately in your browser.
Please fill in the date for the selected mode.
How to use the Pregnancy Due Date Calculator
- Choose the basis: first day of your last period (LMP), conception date, or a known due date.
- Enter the date for that basis.
- For LMP or conception modes, adjust the cycle length if it differs from 28 days.
- Read the estimated due date, today's gestational age in weeks and days, and your trimester.
- Confirm the estimate with your healthcare provider at your dating scan.
Frequently asked questions
How is a due date calculated?
The standard Naegele's rule adds 280 days (40 weeks) to the first day of the last menstrual period. Conception is assumed about 14 days after the LMP, so adding 266 days to a conception date gives the same result. This tool uses exactly those conventions.
How many weeks pregnant am I?
Gestational age counts from the first day of your LMP, so at 40 weeks minus today you are in week 40. The tool reports full weeks plus days (e.g. '15 weeks 3 days'), the way providers and pregnancy apps phrase it.
What if my cycle is not 28 days?
Ovulation typically occurs about 14 days before your next period, so for a 32-day cycle conception is usually around day 18, not day 14. The cycle-length field shifts the conception estimate accordingly, which improves accuracy for longer or shorter cycles.
Why might my ultrasound due date differ?
First-trimester ultrasound measurements of the embryo crown-rump length provide the most accurate dating, and providers may adjust the due date if it differs from the LMP estimate by several days. Ultrasound dating typically replaces the LMP estimate rather than supplementing it.
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