Use this free due date calculator to estimate your pregnancy due date based on the first day of your last menstrual period (LMP). Get your estimated due date, current week of pregnancy, and key trimester milestones all in one place.
Due Date Calculator
| Milestone | Week | Estimated Date |
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How to use this Due Date calculator
1. Enter the first day of your last menstrual period (LMP) — this is the standard starting point used by healthcare providers to calculate a pregnancy due date. If you are unsure of this date, use your best estimate.
2. Click Calculate Due Date to see your estimated due date, current week of pregnancy, and a full timeline of key milestones including trimester transitions, the anatomy scan window, the viability milestone, and full term.
Frequently asked questions
Q: How is the due date calculated?
A: The estimated due date (EDD) is calculated by adding 280 days (40 weeks) to the first day of the last menstrual period. This method, known as Naegele's Rule, assumes a 28-day cycle with ovulation on day 14. Your healthcare provider may adjust your due date based on ultrasound measurements, which are often more accurate — especially when the date of the LMP is uncertain.
Q: How accurate is an estimated due date?
A: Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after the estimated date. The due date is best understood as the midpoint of a normal delivery window rather than a precise target. Babies born between 37 and 42 weeks are considered full term.
Q: What if I have irregular periods?
A: This calculator assumes a regular 28-day cycle. If your cycles are longer or shorter, your actual due date may differ. An early ultrasound (before 14 weeks) is the most accurate way to confirm gestational age and establish a due date when cycle length is irregular or the LMP date is uncertain.
Q: What are the three trimesters?
A: The first trimester covers weeks 1 through 12, the second trimester covers weeks 13 through 27, and the third trimester covers weeks 28 through 40 and beyond. Each trimester involves distinct developmental stages for the baby and different physical experiences for the mother. The anatomy scan is typically performed between weeks 18 and 22.
Q: When is a baby considered full term?
A: A baby is considered full term when born between 39 weeks 0 days and 40 weeks 6 days. Early term is 37 to 38 weeks 6 days, and late term is 41 to 41 weeks 6 days. Babies born before 37 weeks are preterm. Healthcare providers generally avoid elective inductions or cesareans before 39 weeks unless medically necessary.