Pregnancy Due Date Calculator

How It Works

Choose your calculation method — last menstrual period (LMP) or known conception date. The calculator applies standard obstetric formulas: 280 days from LMP (Naegele's rule) or 266 days from conception. It then displays your estimated due date, current gestational age, trimester, and a timeline of prenatal milestones.

Example

If your last menstrual period started on January 1, the calculator adds 280 days to estimate a due date of October 8. At 16 weeks you would be in the second trimester with the anatomy scan approaching around week 20.

When to use this calculator

• Use it as soon as you learn you are pregnant to get an initial due date estimate for planning.
• Use it to understand which trimester you are in and what developmental milestones to expect.
• Use it alongside your healthcare provider's dating to compare LMP-based and ultrasound-based estimates.

Due date calculation methods

• The LMP method (Naegele's rule) adds 280 days to the first day of your last period — it is the most common starting point.
• The conception date method adds 266 days from the estimated day of fertilization, useful when ovulation tracking confirms timing.
• Early ultrasound dating (6–12 weeks) measures crown-rump length and is considered the most accurate method when LMP is uncertain.

Understanding trimesters

• The first trimester (weeks 1–12) covers rapid cell division, organ formation, and the highest risk period for early complications.
• The second trimester (weeks 13–27) brings visible growth, fetal movement, and the anatomy scan ultrasound around week 20.
• The third trimester (weeks 28–40) involves weight gain, lung maturation, and preparation for delivery — most babies are viable from about 34 weeks.

Key prenatal milestones

• Around week 6–7, a heartbeat is usually detectable on ultrasound.
• The anatomy scan at 18–22 weeks checks organ development, growth measurements, and can often reveal the baby's sex.
• From week 36 onward, weekly check-ups are common to monitor the baby's position, growth, and signs of labor readiness.

Preparing for baby

• Start prenatal vitamins (especially folic acid) as early as possible — ideally before conception.
• Build a birth plan and discuss delivery preferences, pain management options, and hospital logistics with your provider.
• Prepare essentials like a car seat, sleeping space, and postpartum support well before the due date to reduce last-minute stress.