📌 Due dates are estimates. Only about 5% of babies are born on their exact due date. Always confirm with your healthcare provider.

About the Due Date Calculator

Finding out you're pregnant is one of life's most profound moments — and one of the first questions that follows is "when is my baby due?" Our Due Date Calculator uses Naegele's rule, the standard obstetrical method, to estimate your expected delivery date based on the first day of your last menstrual period (LMP) or your known conception date.

Beyond just the due date, the calculator shows your current gestational age in weeks and days, which trimester you are in, and key developmental milestones throughout the pregnancy.

How It Works

Enter the first day of your last menstrual period (or your conception date). The calculator adds 280 days (40 weeks) from the LMP date to estimate the due date. If using conception date, it adds 266 days (38 weeks). Gestational age is then calculated from that same LMP baseline.

Formula / Key Reference

Naegele's Rule:

Due Date = LMP + 280 days (40 weeks)

Alternative (conception known):

Due Date = Conception Date + 266 days (38 weeks)

Gestational Age = Current Date − LMP (in weeks and days)

Real-World Example

Last Menstrual Period: July 1, 2025

Estimated Due Date: July 1, 2025 + 280 days = April 7, 2026

As of April 4, 2026 (today):

Gestational age: 39 weeks, 3 days

Trimester: Third trimester

Stage: Full term (37–40 weeks)

Key milestones from this LMP:

End of first trimester (13 weeks): September 30, 2025

Anatomy scan (20 weeks): November 18, 2025

Viability (24 weeks): December 16, 2025

Full term (37 weeks): March 25, 2026

Due date: April 7, 2026

Common Uses

  • Estimating your due date before your first prenatal appointment
  • Tracking gestational age and trimester week by week
  • Planning maternity/paternity leave around the estimated due date
  • Sharing your due date with family and friends
  • Calculating important prenatal screening windows (first-trimester screen, anatomy scan)

Frequently Asked Questions

How accurate is a due date calculator? ▼
The estimated due date is exactly that — an estimate. Only about 4–5% of babies are born on their due date. Most births occur within two weeks before or after. Your OB or midwife will refine the estimate with an early ultrasound measurement, which is generally more accurate than Naegele's rule.
What if my cycle is not 28 days? ▼
Naegele's rule assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, conception (and therefore the due date) shifts accordingly. Enter your cycle length if the calculator offers an adjustment, or discuss the correction with your healthcare provider.
What are the three trimesters? ▼
The first trimester spans weeks 1–13 (months 1–3). The second trimester spans weeks 14–26 (months 4–6). The third trimester spans weeks 27–40+ (months 7–9). Full term is defined as 39–40 weeks. Babies born at 37–38 weeks are early term, and those before 37 weeks are preterm.