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Due Date Calculator

Estimate baby's arrival date

The Due Date Calculator (also known as an EDD Calculator) estimates the day your baby is likely to arrive. It aligns with the standard medical dating assigned by your OB/GYN using the date of your last period.

Inputs Explained

  • First Day of Last Period (LMP): The standard start date for all pregnancy math. Do not enter the date of conception (unless using a specialized IVF tool).
Result
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Formula

Due Date = LMP + 280 days
(40 weeks from last period)
Conception ≈ LMP + 14 days

Pregnancy Timeline

First Trimester Weeks 1-12
Second Trimester Weeks 13-26
Third Trimester Weeks 27-40
Full Term 39-40 weeks

Related

Pregnancy Weeks CalculatorConception CalculatorOvulation Calculator

Complete Guide to Your Due Date (EDD)

Your Estimated Due Date (EDD) is a projection of the day your labor might begin. Most pregnancies last 40 weeks (280 days) from the first day of your last menstrual period (LMP).

How it Works: Naegele's Rule

The standard formula used by doctors worldwide is called Naegele's Rule. Here is how you can calculate it yourself:

  1. Start with the first day of your last period.
  2. Add 7 days.
  3. Subtract 3 months.
  4. Add 1 year.

Step-by-Step Example

Let's calculate a due date:

  • LMP: November 1st, 2025.

Calculation:

  1. Add 7 days: Nov 1 + 7 = Nov 8.
  2. Subtract 3 months: Nov -> Oct -> Sep -> August.
  3. Add 1 year (to the next cycle): August 8th, 2026.

Why is it 40 Weeks?

Pregnancy actually lasts about 38 weeks from conception. However, because it is hard to know exactly when ovulation occurred, doctors add 2 weeks to account for the time between your last period and ovulation. Correcting for this "phantom" time gives us the standard 40-week timeline.

Use Cases for Knowing Your Due Date

  • Maternity Leave: Planning when to stop working and arranging childcare.
  • Trimester Tracking: Knowing when you enter the "safe zone" of the second trimester (13 weeks).
  • Hospital Planning: Scheduling tours and pre-registering at your delivery center.

Pregnancy Milestones by Trimester

  • 🌱 First Trimester (Weeks 1-12): The baby's major organs form. Morning sickness is common.
  • 👶 Second Trimester (Weeks 13-26): The "honeymoon phase." You feel the baby move (quickening) and can determine gender.
  • 🤰 Third Trimester (Weeks 27-40): Baby gains weight rapidly. Braxton Hicks contractions may start.
Medical Disclaimer: Your due date is an estimate. Only ~5% of babies are born on that exact day. Most arrive within a 2-week window before or after. Trust your doctor's ultrasound dating over LMP if there is a discrepancy.

Frequently Asked Questions

We use Naegele's Rule: add 7 days to the first day of your last menstrual period (LMP), then subtract 3 months. This equals LMP + 280 days (40 weeks).

Yes, if you know the exact date of conception (e.g., IVF), you can add 266 days (38 weeks) to find your due date. Most pregnancies are dated from LMP since exact conception is hard to pinpoint.

An early ultrasound (8-12 weeks) is more accurate than LMP for dating. If the baby measures significantly larger or smaller than expected based on LMP, your doctor may update your estimated due date.

Yes, 40 weeks is the standard full term. However, anything from 37 to 42 weeks is considered a normal window for delivery. Only ~4-5% of babies are born on their exact due date.

First Trimester: Weeks 1-12. Second Trimester: Weeks 13-26. Third Trimester: Weeks 27-40+. Each brings different developmental milestones and symptoms.

References

Pregnancy dating and milestones are based on standard obstetrical guidelines:

  • American College of Obstetricians and Gynecologists (ACOG). "Methods for Estimating the Due Date". Committee Opinion No. 700.
  • Mayo Clinic. "Pregnancy due date calculator: How is my due date calculated?".
  • National Institutes of Health (NIH). "Pregnancy: Conception to Birth".