Pregnancy Due Date Calculator
Your estimated due date from your last period, conception date, IVF transfer or dating scan, how many weeks and days pregnant you are today, and a timeline of scans and milestones.
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How to work out your due date
- Choose what to work it out from: your last period, conception date, IVF transfer, a dating scan or a due date you already know.
- Enter the date, plus your cycle length, embryo age or scan result if asked.
- Read your due date, how many weeks pregnant you are today and your timeline of scans.
How the due date is worked out
Pregnancy is counted from the first day of your last menstrual period (LMP), about two weeks before conception, so the standard due date is LMP + 280 days (40 weeks), known as Naegele's rule. If your cycles are usually longer or shorter than 28 days, ovulation shifts by the difference, so the due date moves with it (a 32-day cycle adds 4 days). From a known conception date, the due date is 266 days (38 weeks) later. For IVF, it's 261 days after a 5-day blastocyst transfer, 263 days after a 3-day transfer and 260 after a 6-day one. A dating scan measures the baby to estimate how far along you are; if it differs from your period-based date, maternity services usually go by the scan.
Only about 1 in 20 babies arrive on their due date; most come between 37 and 42 weeks. The timeline shows the windows the NHS uses for the dating scan (10 weeks to 14 weeks), the mid-pregnancy scan (18 weeks to 20 weeks 6 days) and term (37 weeks onwards); other countries' schedules differ slightly. This tool is for planning and interest only. Your midwife, GP or doctor will confirm your dates. Everything is worked out in your browser and nothing is saved or sent.
Questions about due dates
How is a due date calculated?
40 weeks (280 days) from the first day of your last period, known as Naegele’s rule. If your cycle is longer or shorter than 28 days, the date moves by the difference.
How many weeks pregnant am I?
Pregnancy is counted from the first day of your last period, so at conception you’re already about 2 weeks pregnant. The calculator shows weeks and days for today.
How accurate is my due date?
It’s an estimate: only about 1 in 20 babies arrive on the day. Most are born between 37 and 42 weeks. If a dating scan gives a different date, maternity services usually go by the scan.
How is an IVF due date worked out?
From the transfer date: 261 days after a 5-day blastocyst transfer, 263 days after a 3-day transfer and 260 after a 6-day transfer.