calculate due date

How due date calculation works

Most pregnancies are dated to 40 weeks (280 days) from the first day of your last menstrual period. That date is called the estimated due date (EDD). It is an estimate, not a deadline—only a small percentage of babies arrive on the exact calculated date.

The calculator above uses common clinical rules so you can quickly estimate your due date from your period, conception date, or IVF transfer details. This gives you a useful planning timeline for prenatal visits, tests, and maternity leave discussions.

3 common ways to calculate a due date

1) Last menstrual period (LMP)

This is the standard method in most pregnancies. The formula starts at day 1 of your last period, then adds 280 days. If your menstrual cycles are usually longer or shorter than 28 days, the estimate can be adjusted.

• 28-day cycle: add 280 days
• Longer cycle: due date may be later
• Shorter cycle: due date may be earlier

2) Conception date

If you know the likely conception date, the due date is estimated by adding 266 days (38 weeks). This can be helpful when ovulation timing is known through cycle tracking or fertility monitoring.

3) IVF transfer date

IVF dating can be very precise because embryo development is known. The calculator accounts for embryo age at transfer and estimates the due date using standard obstetric conventions.

Why your due date can change

Early ultrasound is often used to confirm gestational age. If ultrasound measurements differ significantly from cycle-based dating, your clinician may update the estimated due date. That is normal and helps align care with fetal development.

• Irregular cycles can make LMP dating less accurate
• Uncertain ovulation timing can shift estimates
• Early ultrasound can improve precision

What to expect by trimester

First trimester (0-13 weeks)

• Initial prenatal intake and health history
• Baseline bloodwork and early screening
• Nausea, fatigue, and breast tenderness are common

Second trimester (14-27 weeks)

• Anatomy ultrasound is often done around 18-22 weeks
• Energy may improve for many people
• Fetal movement is commonly felt during this period

Third trimester (28-40+ weeks)

• More frequent prenatal visits
• Birth planning and hospital preparation
• Monitoring fetal growth and maternal wellbeing

Important reminders

A due date is best treated as a target window. Many healthy births occur before or after the exact date. If you have pain, bleeding, severe headache, fluid leakage, reduced fetal movement, or any urgent concern, contact your healthcare team immediately.

This calculator is educational and does not replace medical advice. For personalized guidance, always follow your OB-GYN, midwife, or fertility specialist.