Pregnancy Due Date

One of the first questions every expecting parent asks is: when is my baby due? The most widely used method for estimating a due date is Naegele's rule, a formula developed in the 19th century that adds 280 days (40 weeks) to the first day of a woman's last menstrual period (LMP). It remains the standard estimation method used by obstetricians, midwives, and pregnancy apps worldwide, even though it's based on a simplification — it assumes a textbook 28-day menstrual cycle with ovulation occurring on day 14.

Our pregnancy due date calculator applies Naegele's rule automatically. Enter the first day of your last menstrual period (or, if you know it, your conception date or IVF transfer date), and the tool instantly calculates your estimated due date, how many weeks and days pregnant you currently are, which trimester you're in, and key milestone dates like the end of the first trimester and the start of the third. This saves you from counting weeks on a paper calendar or doing the 280-day addition by hand.

It's important to understand that a due date is an estimate, not a guarantee — only about 4-5% of babies are actually born on their exact calculated due date. Most babies arrive within a window of two weeks before to two weeks after the estimated date. If you have irregular cycles, know your exact conception date, or your pregnancy was conceived via IVF, your healthcare provider may adjust your due date using an early ultrasound, which is generally considered more accurate than LMP-based dating alone, especially when cycles are irregular.

Knowing an accurate estimated due date shapes nearly every part of prenatal care and planning:

Prenatal care scheduling: Your due date determines the timing of key screening tests, such as first-trimester genetic screening (typically weeks 10-13), the anatomy ultrasound (weeks 18-22), and glucose screening for gestational diabetes (weeks 24-28). Providers schedule these windows based on gestational age.

Monitoring fetal development: Each week of pregnancy corresponds to specific developmental milestones. Knowing your current gestational week helps you understand what's happening and what symptoms are expected at each stage.

Leave and life planning: Parents use the due date to plan parental leave, notify employers, arrange childcare, and prepare the home — all of which benefit from as much advance notice as possible.

Identifying preterm or post-term risk: A pregnancy is considered full-term between 39 and 40 weeks, preterm before 37 weeks, and post-term after 42 weeks. Tracking gestational age against the due date helps your care team flag pregnancies that may need closer monitoring.

Important: This calculator provides an estimate for informational purposes only and is not a substitute for professional medical advice. Always confirm your due date and gestational age with your doctor or midwife, who may adjust the estimate based on ultrasound measurements, especially if your cycles are irregular.