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Online Calculators
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Pregnancy & Due Date Calculator

Calculate your due date, see how many weeks pregnant you are, and estimate birth probability by week.

How to Use

  1. 1

    Choose your calculation method: Last Menstrual Period (LMP) or Ultrasound

  2. 2

    If using LMP: enter the first day of your last period and select your cycle length

  3. 3

    If using Ultrasound: enter the scan date and gestational age at the time of scan

  4. 4

    View your estimated due date, current week, trimester, and birth probability chart

Examples

Good Examples

Last period started January 1, 2026 (28-day cycle)

Due date: October 8, 2026 (280 days from LMP)

Ultrasound at week 10 on March 15, 2026

Estimated LMP: January 3, 2026 → Due date: October 10, 2026

Bad Examples

Forgetting to adjust for cycle length

A 32-day cycle shifts the due date by ~4 days later

Expecting baby on exact due date

Only ~5% of babies arrive on the predicted due date

Common Mistakes

  • Not adjusting for cycle length — Naegele's Rule assumes a 28-day cycle
  • Confusing conception date with due date — conception occurs ~2 weeks after LMP
  • Expecting the due date to be exact — babies arrive within a 2-week window most of the time
  • Using ultrasound weeks as calendar weeks — ultrasound measures gestational age from estimated LMP

Frequently Asked Questions

Q

How is my due date calculated?

Your due date is calculated using Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period. If you know your cycle is longer or shorter than 28 days, the calculator adjusts accordingly.

Q

How accurate is the due date?

Only about 5% of babies are born on their exact due date. Most babies arrive within a 2-week window before or after. The due date is best used as an estimate for planning purposes.

Q

When does each trimester start?

First trimester: weeks 0–12, Second trimester: weeks 13–27, Third trimester: weeks 28–40+. Each trimester is roughly 13–14 weeks long.

Q

Can I calculate my due date from an ultrasound?

Yes — if you know the date of your ultrasound and the gestational age measured at that scan, the calculator can work backwards to estimate your LMP and due date. This often yields a more accurate result than LMP alone.