Pregnancy Calculator: Estimate Your Due Date

Track your journey from conception to delivery.

The most exciting part of pregnancy is knowing when you’ll finally meet your little one. Our Pregnancy Calculator uses the standard medical methods—including Naegele’s Rule—to estimate your due date, current gestational age, and key developmental milestones.

Pregnancy Calculator

Estimate your due date and track progress

familyhealthcalc.com

Select your LMP to see your journey

pregnancy

How the Calculation Works

Most pregnancies last approximately 40 weeks (280 days) from the first day of your last menstrual period.

Naegele’s Rule

This is the classic formula used by healthcare providers in the US and UK:

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

Important Pregnancy Milestones

  • End of 1st Trimester: Week 12 (Organ development complete).
  • Anatomy Scan: Weeks 18–22 (The “big” ultrasound).
  • Age of Viability: Week 24 (The point where a baby has a chance of survival outside the womb).
  • Full Term: Week 39 (The baby is fully developed and ready for birth).

Trimester Breakdown

Pregnancy is divided into three distinct phases:

  1. First Trimester (Weeks 1–12): A period of rapid development and hormonal changes.
  2. Second Trimester (Weeks 13–26): Often called the “golden phase” as morning sickness typically fades and you begin to feel the baby move.
  3. Third Trimester (Weeks 27–40+): The final stretch where the baby gains weight rapidly, and your body prepares for labor.

1. How accurate is my due date?

Only about 4% to 5% of babies are born exactly on their due date. Most babies arrive between two weeks before and two weeks after the estimated date. In the UK and Canada, medical professionals often refer to it as an “estimated window” rather than a fixed deadline.

2. What if I don’t know the date of my last period?

Don’t worry! If your periods are irregular or you simply don’t remember, your doctor will perform a dating ultrasound (usually between weeks 8 and 14) to measure the “crown-rump length” of the baby. This is considered the most accurate way to determine gestational age.

3. Can the due date change later in pregnancy?

While the date is rarely “moved” after the first trimester scan, your doctor may adjust your care plan if the baby is measuring significantly larger or smaller than expected during late-stage checkups.

4. How long is a “normal” pregnancy?

While 40 weeks is the average, a “full-term” pregnancy is anything between 39 weeks 0 days and 40 weeks 6 days.