Due Date Calculator
Estimate your baby's due date from your last menstrual period or conception date.
The Formula
Due Date = LMP + 280 days
From conception date:
Due Date = Conception + 266 days
280 days = 40 weeks = ~9 months 7 days
+ 280 days
Due Date: October 8, 2026
First trimester ends: ~April 1
Second trimester ends: ~July 1
How Due Dates Are Calculated
A typical pregnancy lasts 280 days (40 weeks) from the first day of the last menstrual period (LMP). This is called Naegele'
How the Due Date Calculator Works
Enter the first day of your last menstrual period (LMP) or your conception date, along with your average cycle length. The calculator estimates your due date and key pregnancy milestones.
About Due Date Accuracy
Due dates are estimates. Only about 5% of babies are born on their exact due date. Most deliveries happen within two weeks before or after the estimated date.
Frequently Asked Questions
What is Naegele's Rule?
Naegele's Rule is the standard due date calculation: take the first day of your last menstrual period, add 7 days, then add 9 months (or equivalently, add 280 days). It assumes a 28-day cycle with ovulation on day 14. If your cycle is regularly longer or shorter, adjust accordingly — for example, a 35-day cycle pushes the estimated due date 7 days later.
How accurate is an ultrasound due date?
A first-trimester ultrasound performed before 13 weeks is the most accurate dating method, typically within 5–7 days. Between 13–20 weeks, accuracy is within 7–10 days. After 20 weeks, ultrasound dating becomes progressively less accurate because fetal size varies more between individuals. Most providers set a final due date based on the earliest ultrasound if it differs significantly from the LMP calculation.
What does it mean to be 40 weeks pregnant?
At 40 weeks, you are at your estimated due date. At this point the baby is considered full term (full term is actually 39–40 weeks; late term is 41 weeks; post term is 42+ weeks). Most providers monitor pregnancies closely after 40 weeks and discuss induction options typically between 41 and 42 weeks, as risks for certain complications increase modestly past 41 weeks.
When should I call my doctor after learning I am pregnant?
Most providers recommend scheduling a first prenatal appointment between 8–10 weeks of pregnancy. If you have a history of pregnancy complications, fertility treatments, or any concerning symptoms (heavy bleeding, severe pain), contact your provider sooner. The first appointment typically includes confirming the pregnancy, dating the gestational age, and ordering initial bloodwork.
Can I calculate my due date from a positive pregnancy test?
Not directly — a positive test confirms pregnancy but does not tell you how far along you are. You need either the date of your last menstrual period or a conception date. If you know when you conceived (through IVF transfer, ovulation tracking, or other methods), add 266 days for the estimated due date. Otherwise, enter your LMP date in this calculator.