EDD (estimated due date): what it means and how your doctor works it out

EDD stands for estimated due date, the day your baby is expected if your pregnancy runs 40 weeks. KKH's obstetrics team explains that the 40 weeks are counted from the first day of your last menstrual period, not from conception, and your doctor then checks the date against an early scan. Treat it as a target. Cleveland Clinic says only about 5% of babies arrive on the day.

How your EDD is calculated

Nobody knows the exact day you conceived, so doctors count from a date you do know. KKH's obstetrics team says a pregnancy really lasts about 38 weeks (266 days) from conception, but the 40 week count from your LMP is used because the conception date is usually unknown.

Cleveland Clinic gives a quick way to do it by hand: take the first day of your last period, add seven days, count back three months and add a year. If your period started on 10 January 2026, that gives 17 October 2026. Our due date calculator does the same sum and lets you adjust for a longer or shorter cycle.

Why the dating scan can move it

Your first EDD is a starting point. KKH's obstetrics team says it can be corrected using the first major ultrasound, the dating scan, which can happen from week 7. KKH lists the dating scan among its first trimester tests, and SingHealth places it at weeks 8 to 12.

The NHS says a scan estimates how many weeks pregnant you are more accurately than the date of your period. If your own sums and the scan disagree, the date your doctor writes down after the scan is the one to use. Your gestational age follows from it.

If your baby is early or late

The NHS says pregnancy normally lasts from 37 to 42 weeks from the first day of your last period, so a baby born a couple of weeks either side of the EDD is still within the normal range. SingHealth says your pregnancy counts as full term after week 37.

If your EDD passes, KKH says first-time mums often deliver later and anything before 42 weeks is acceptable. Your doctor will watch you and your baby more closely, which may mean another scan and more clinic visits. If your doctor raises induction of labour, read that page before you decide. Our 40 weeks pregnant guide covers that week in detail.

Frequently asked questions

What does EDD mean in pregnancy?

Estimated due date. It is the day you reach 40 weeks, counted from the first day of your last period. On KKH paperwork it may read estimated delivery date, which is the same thing.

How accurate is my EDD?

It is an estimate. Cleveland Clinic says about 5% of babies are born on the date itself, and the NHS says a normal pregnancy lasts anywhere from 37 to 42 weeks.

Can my EDD change?

Yes. KKH's obstetrics team says your doctor can correct it after the dating scan.

What if I don't remember the date of my last period?

The NHS says to speak to a midwife or GP. In Singapore that means your gynae or polyclinic doctor, who will date the pregnancy from an ultrasound instead.

Related terms

• LMP (Last Menstrual Period): The first day of your last period before pregnancy. Your week count and due date are worked out from it.
• Gestational Age: How far along your pregnancy is, in weeks and days, counted from the first day of your last period.
• Trimester: One of the three stages of pregnancy, each about three months long.
• Induction of Labour: Starting labour with medical help, such as a pessary, balloon or drip, instead of waiting for it to begin.
• Antenatal (also Prenatal): Antenatal means before birth. Antenatal care is the check-ups, scans and tests you get while you are pregnant.

See every term in the glossary