Pregnancy Due Date Calculator

Enter your last period date or conception date to instantly calculate your estimated due date (EDD), current pregnancy week, trimester, and a full milestone timeline — including key appointment windows. Free, no sign-up.

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How to Calculate Your Due Date

  1. Select whether you know your Last Menstrual Period (LMP) or Conception Date.
  2. Enter the date and your typical cycle length if using LMP.
  3. Click Calculate Due Date to see your EDD, pregnancy week, trimester, and full milestone calendar.

How Due Dates Are Calculated

The standard method for calculating a due date is Naegele's Rule, named after the 19th-century obstetrician Franz Karl Naegele. The formula: add 280 days (40 weeks) to the first day of your last menstrual period. This works because pregnancy is counted from the LMP rather than from the actual moment of conception — adding approximately 2 weeks to account for the time between menstruation and ovulation.

The 40-week count covers the full gestational period: two weeks of the menstrual cycle before conception, about 38 weeks of actual fetal development. Most healthy pregnancies deliver anywhere between 37 and 42 weeks. Only about 1 in 20 babies arrives precisely on the calculated due date.

For the most accurate dating, healthcare providers use a combination of LMP calculation and an early ultrasound (ideally before 14 weeks). The ultrasound measures the baby's crown-rump length, which can adjust the due date by a few days to two weeks depending on actual fetal size.

Frequently Asked Questions

How is a pregnancy due date calculated? ▼

A pregnancy due date (EDD — Estimated Due Date) is calculated using Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a standard 28-day cycle with ovulation on day 14.

How accurate is an estimated due date? ▼

Only about 5% of babies are born exactly on their due date. The EDD is a statistical midpoint — about 80% of births occur within 2 weeks before or after the due date. Your OB or midwife will refine your due date with an early ultrasound.

What is the difference between LMP and conception date? ▼

Your LMP (Last Menstrual Period) is the first day of your last period — typically about 2 weeks before conception. The conception date is when fertilization actually occurred. Our calculator accepts both and automatically adjusts the calculation.

How does cycle length affect my due date? ▼

A standard 28-day cycle is assumed for most due date calculations. If your cycle is longer (e.g., 35 days), ovulation — and likely conception — occurs later, so your due date is pushed forward. Our LMP method accounts for this.

What are the three trimesters of pregnancy? ▼

The first trimester covers weeks 1–12. The second trimester covers weeks 13–26. The third trimester covers weeks 27–40 (or until birth). Each trimester brings distinct developmental milestones and different prenatal care focuses.

When is "full term" pregnancy? ▼

Full term is defined as 39–40 weeks of pregnancy. 'Early term' is 37–38 weeks, 'full term' is 39–40 weeks, 'late term' is 41 weeks, and 'post-term' is 42+ weeks. Babies born before 37 weeks are considered premature.

When should I schedule my first prenatal appointment? ▼

Most healthcare providers recommend scheduling your first prenatal appointment between weeks 8 and 10. The visit typically includes confirmation of the pregnancy, a review of your medical history, first blood work, and discussion of prenatal vitamins.

What is the anatomy scan? ▼

The anatomy scan (also called the 20-week scan) is a detailed ultrasound performed between weeks 18 and 20. It checks the development of the baby's organs, measures growth, checks amniotic fluid levels, and can reveal the sex of the baby if desired.

What does "weeks + days" mean in pregnancy tracking? ▼

Pregnancy weeks are counted from the first day of your LMP. "Week 8+3" means 8 complete weeks and 3 additional days of pregnancy — a total of 59 days. Healthcare providers use this exact notation.

Is this due date calculator safe to use for medical decisions? ▼

This calculator provides an estimate for informational purposes only. Always confirm your due date with a qualified healthcare provider, especially via early ultrasound. Medical decisions about your pregnancy should be made with professional guidance.