Pregnancy Due Date Calculator
Work out your estimated due date from your last period, conception date or IVF transfer, plus how far along you are and your key pregnancy dates.
Verified October 2026 · Sources: ACOG Committee Opinion 700 (estimating the due date); ACOG Committee Opinion 579 (term definitions); NHS due date calculator; NHS scans
- Entering the last day of your period, or the date of a positive test — use the FIRST day of your last period.
- Ignoring a long or short cycle — adjust the cycle length so the date shifts correctly.
- Counting from conception and then adding 40 weeks — from conception it's 38 weeks (266 days).
- Treating the due date as fixed — your dating scan date takes priority, and 37–42 weeks is normal.
- →Book antenatal care with your GP, midwife or obstetrician as soon as you know you're pregnant.
- →Take a daily 400 microgram folic acid supplement until 12 weeks, as the NHS advises.
- →Ask your care provider about the dating scan — it confirms how far along you are.
- →Contact your maternity unit urgently about bleeding, severe pain, fluid leaking or reduced baby movements.
This tool is for informational purposes only. Always verify results with a qualified professional.
What is the Pregnancy Due Date Calculator?
A pregnancy due date calculator estimates the day your baby is due — the estimated due date (EDD) or estimated date of delivery. By convention, pregnancy is counted from the first day of your last menstrual period (LMP), not from conception, so a full-term pregnancy is about 40 weeks or 280 days long even though the baby has been developing for about 38 weeks. This calculator gives you the due date, how many weeks and days pregnant you are today, your trimester, and a timeline of key dates such as scan windows and when you reach full term.
From your last period, the calculator uses Naegele's rule: LMP + 280 days, which is the same as adding one year, subtracting three months and adding seven days. Naegele's rule assumes a 28-day cycle with ovulation on day 14, so if your cycles are regularly longer or shorter the due date is moved by the difference — a 32-day cycle adds 4 days, a 25-day cycle takes away 3 days. From a known conception date, the due date is conception + 266 days (38 weeks). For IVF, the American College of Obstetricians and Gynecologists (ACOG) dates the pregnancy from the embryo transfer: add 261 days for a day-5 (blastocyst) transfer or 263 days for a day-3 transfer.
Worked example: if the first day of your last period was 6 January 2026 and your cycle is 28 days, your estimated due date is 13 October 2026 (6 January + 280 days). With a 32-day cycle it moves to 17 October 2026. A day-5 embryo transfer on 20 January 2026 gives a due date of 8 October 2026, and a known conception date of 20 January 2026 gives 13 October 2026.
Trimesters are counted from the same starting point: the first trimester runs to the end of week 13, the second from 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks to birth. ACOG describes 37 weeks 0 days to 38 weeks 6 days as early term, 39 weeks 0 days to 40 weeks 6 days as full term, 41 weeks as late term and 42 weeks onwards as post-term. The NHS notes that pregnancy normally lasts between 37 and 42 weeks from the first day of the last period, so the due date is a guide rather than an appointment — most babies arrive within a couple of weeks either side.
An early ultrasound measurement is the most accurate way to date a pregnancy. In the UK the dating scan is offered at around 10–14 weeks, and ACOG advises that ultrasound in the first trimester is the most accurate method to establish or confirm gestational age. If the scan date differs from your LMP date, your midwife or doctor will usually go by the scan, so use the date they give you for appointments and planning. This calculator is informational only and cannot confirm a pregnancy or replace antenatal care.
How to Use This Calculator
- 1Choose how you want to calculate: first day of your last period, conception date, or IVF embryo transfer date.
- 2Enter the date. For the period method, also enter your usual cycle length (28 days if you're not sure).
- 3For IVF, choose whether it was a day-5 (blastocyst) or day-3 embryo transfer.
- 4Read your estimated due date, how many weeks and days pregnant you are today, and your trimester.
- 5Check the milestone timeline for scan windows, trimester changes and full term, each with its exact date.
- 6Copy the result to share, and confirm your due date with your midwife or doctor after your dating scan.