Pregnancy Due Date Calculator – EDD, IVF, Scans & Maternity Leave
Calculate your estimated due date from your last menstrual period or IVF transfer date. Get your full pregnancy timeline including trimester dates, NHS scan windows, maternity leave start date, and how many weeks pregnant you are today.
How Your Due Date Is Calculated
The standard method uses Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the calculator adjusts accordingly — for a 35-day cycle, ovulation occurs around day 21, shifting your EDD forward by seven days.
Your dating scan at 10–14 weeks may revise your EDD based on the baby's crown-rump length (CRL), which is more accurate than LMP dating in the first trimester. Always use your scan-confirmed EDD for planning.
IVF due date calculation: For IVF pregnancies, the due date is calculated from the egg retrieval date (day 0) or embryo transfer date. A Day 3 embryo transfer: add 263 days (37 weeks + 4 days) to transfer date. A Day 5 blastocyst transfer: add 261 days (37 weeks + 2 days). The calculator handles both.
NHS Antenatal Appointments
- Booking appointment (8–10 weeks): Your first midwife appointment. Book as soon as you have a positive test.
- Dating scan (10–14 weeks): Confirms EDD and screens for chromosomal conditions. Usually around 12 weeks.
- Combined screening test (10–14 weeks): Optional blood test + nuchal translucency scan for Down's syndrome risk.
- Mid-pregnancy anomaly scan (18–21 weeks): Checks for structural abnormalities. Often called the 20-week scan.
- Growth scans (28–36 weeks): Additional scans if indicated — not routine for all pregnancies.
- Term scan (36–40 weeks): Checks position of baby and placenta before birth.
Maternity Leave Planning
In the UK, compulsory maternity leave starts 2 weeks before your due date (4 weeks if you work in a factory). However, you can choose to start maternity leave from 11 weeks before your due date. Your employer must be notified of your intended start date at least 15 weeks before your due date. The calculator shows the earliest and latest maternity leave start dates and the compulsory start window.
SMP qualifying week: To qualify for Statutory Maternity Pay, you must have been continuously employed for 26 weeks by the 15th week before your due date — known as the Qualifying Week. This calculator shows that date so you can confirm eligibility.