Pregnancy Due Date Calculator

A pregnancy due date calculator is a tool that estimates a due date, trimester dates, and gestational week from last menstrual period or conception date using Naegele's Rule. Enter those dates — this page does not replace prenatal care.

This is an estimate from the dates you enter — not medical advice. A modeled due date is not a diagnosis; confirm with a clinician.

Before your first prenatal appointment. Get an early due date estimate to share with your doctor and use as a reference before your dating ultrasound confirms the date.

Tracking trimester transitions. See estimated dates for when your second trimester starts, when the anatomy scan window typically opens, and when the third trimester begins — helpful for planning appointments and conversations around these milestones (due dates are estimates).

Cycle-based planning. Enter a hypothetical LMP date to estimate when a baby conceived in a given cycle would be due — useful for family planning timelines.

The standard method for calculating a baby's arrival is based on Naegele's Rule. This math assumes a 280-day (40-week) pregnancy from the first day of your last menstrual period (LMP). While this is the industry standard for OBGYNs, this Pregnancy Due Date Calculator also allows you to adjust for your unique cycle length, providing a more personalized estimate.

Pregnancy is divided into three distinct phases, each roughly 12–14 weeks long. This tool calculates these dates automatically:

• First Trimester (Week 1–12): A time of rapid cellular development. Most women discover they are pregnant during this phase.
• Second Trimester (Week 13–26): Often called the "honeymoon phase," as morning sickness usually fades and energy returns.
• Third Trimester (Week 27–40+): The final stretch where the baby finishes growing and prepares for the outside world.

1. Start Prenatal Vitamins: Folic acid is critical in the first few weeks for neural tube development. Consult your doctor immediately to find the right supplement.
2. Track Your Symptoms: Keep a log of your energy levels, cravings, and any spotting. This data is incredibly helpful for your first prenatal appointment.
3. Verify with Ultrasound: While LMP math is great, a "dating scan" (ultrasound) performed between weeks 8 and 12 is considered the most accurate way to confirm a due date.

If your LMP started January 15, 2026: add 280 days for a due date of October 22, 2026. Naegele's shortcut: subtract 3 months (October 15), add 7 days (October 22). Naegele's Rule is the clinical standard used by ACOG (American College of Obstetricians and Gynecologists).

For general date arithmetic around your pregnancy timeline, the Date Calculator can count days between any two dates — useful for counting calendar days until your estimated due date or between appointments. The Age Calculator can help you work out how old your child will be at any future milestone date.

The due date method used in this calculator follows ACOG — Estimating Due Date, the authoritative clinical guidance on gestational dating from the American College of Obstetricians and Gynecologists.