Pregnancy Due Date Calculator
Last updated: June 8, 2026Estimate your baby's due date from your last period.
The Pregnancy Due Date Calculator estimates when your baby is due from the first day of your last menstrual period (LMP) using Naegele's rule — LMP plus 280 days. Enter one date and it instantly shows your estimated due date, approximate conception date (LMP + 14 days), which trimester you're in, and how many weeks and days pregnant you are today. It runs entirely in your browser, free, with no sign-up and nothing uploaded.
Disclaimer: This calculator gives general estimates for informational purposes only and is not medical advice. Results vary by individual, measurement method and formula. Always consult a qualified healthcare professional before making decisions about your health, diet or fitness.
How to use Pregnancy Due Date Calculator
Working out your due date takes one piece of information: the first day of your last period. From that single date the calculator applies Naegele's rule and a standard 40-week (280-day) pregnancy to project your due date, estimate conception, and tell you where you are right now. Everything is computed locally in your browser, so no personal dates are ever sent anywhere.
Read the full guide: How to Calculate Your Due Date (Free Pregnancy Tool)
- 1Open the date picker and select the first day of your last menstrual period (LMP) — not the day it ended.
- 2The calculator adds 280 days to give your estimated due date and shows it in plain language.
- 3Read your estimated conception date, your current trimester, and how many weeks and days pregnant you are today, all updated instantly.
One date in, four answers out
A single LMP entry returns your due date, conception estimate, trimester and current weeks-pregnant together, with no forms to fill or button to press.
Real Naegele's rule
It uses the same LMP-plus-280-days method clinicians use for a first dating estimate, assuming a regular 28-day cycle with ovulation around day 14.
Completely private
Your period date never leaves your device — the whole calculation runs in your browser with no account and nothing uploaded.
Find out how many weeks pregnant I am
If you know your last period started a while ago but aren't sure how far along you are, enter that date and the calculator counts forward to today, showing your progress as exact weeks and days pregnant — handy for booking your first midwife or prenatal appointment.
Estimate my due date from LMP
The classic use: you have the first day of your last period and want a target date for the birth. The tool applies the 280-day Naegele calculation and gives you a clear estimated due date, plus the trimester you're currently in, so you can start planning leave and appointments.
Work out when I conceived
To estimate conception for your own records or to narrow a likely window, the calculator adds two weeks to your LMP — the point in a typical 28-day cycle when ovulation occurs. It's an estimate, not proof of a specific date, but it answers the common 'roughly when did this happen' question.
Plan around each trimester
Knowing whether you're in the first, second or third trimester helps you anticipate scans, screening windows and what to expect next. Enter your LMP and the tool labels your current trimester and weeks pregnant, giving you a quick reference point between checkups.
Pregnancy Due Date Calculator — frequently asked questions
How is the due date calculated?
By Naegele's rule: it adds 280 days (40 weeks) to the first day of your last menstrual period. This is the standard way to date a pregnancy before an ultrasound, assuming a regular 28-day cycle.
How accurate is an LMP due date?
It's a solid estimate, but only about 4 in 100 babies arrive on the exact date. Most are born within two weeks either side. If your cycle is irregular or longer than 28 days, an early ultrasound gives a more accurate date.
How is the conception date worked out?
It adds 14 days to your LMP, since ovulation and conception typically happen around day 14 of a 28-day cycle. It's an approximation — actual conception can vary by several days depending on when you ovulated.
How do you know which trimester I'm in?
From today's date minus your LMP: weeks 0–12 are the first trimester, 13–26 the second, and 27 onward the third. The tool also shows your exact weeks and days pregnant as of today.
Is my information private?
Yes. The calculation happens entirely in your browser, so your last-period date is never uploaded or stored, and no sign-up is required. It's free to use.
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