A pregnancy due date calculator estimates when your baby will arrive based on the first day of your last menstrual period (LMP) or a known conception date. The standard calculation — called Naegele's Rule — adds 280 days (40 weeks) to your LMP date, producing an estimated due date that your OB-GYN will also use at your first prenatal appointment.

This tool also adjusts for non-standard cycle lengths, calculates your trimester start dates, and shows your current gestational week — giving you a complete picture from a single date entry. All calculations run locally in your browser; no health data is stored or transmitted.

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. Know exactly when your second trimester starts, when the anatomy scan window opens, and when the third trimester begins — plan appointments and conversations around these milestones.

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 that a pregnancy lasts exactly 280 days (40 weeks) 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.