Due Date Calculator
Calculate your pregnancy due date from LMP, conception, or ultrasound
Estimated Due Date
How to Use
- Select the calculation method: LMP date, Conception date, or Ultrasound dating.
- For LMP method, enter the first day of your last menstrual period.
- For Conception method, enter the date of conception (this is 14 days after LMP on average).
- For Ultrasound method, enter the ultrasound date and the gestational age determined at that scan.
- Click 'Calculate Due Date' to see your estimated due date and trimester dates.
About Due Date Calculation
Three Calculation Methods
The LMP method (Naegele's rule: LMP + 280 days) is the standard approach used in most pregnancies. Conception date method adds 266 days to the conception date. Ultrasound dating is the most accurate method, using fetal measurements to estimate gestational age. An early ultrasound (before 14 weeks) can revise the due date.
Accuracy of Each Method
LMP method assumes a regular 28-day cycle with ovulation on day 14 — accuracy decreases with irregular cycles. Conception dating requires knowing the exact conception date, which is rarely known precisely. Ultrasound dating is most accurate in the first trimester (±5 days) and becomes less precise as pregnancy progresses.
Trimester Dates
First trimester: weeks 1–12 (days 1–84). Second trimester: weeks 13–26 (days 85–182). Third trimester: weeks 27–40 (days 183–280). These dates are calculated from the first day of the LMP. The second trimester often brings relief from morning sickness, while the third involves rapid fetal growth.
When Babies Actually Arrive
Only about 5% of babies arrive on their exact due date. 80% arrive within 2 weeks before or after the due date. Births at 37–42 weeks are considered full-term. Preterm birth is before 37 weeks, and post-term is after 42 weeks. A due date is best considered a due 'period' rather than an exact day.
Key Features
- Supports three different calculation methods
- Shows complete trimester date ranges
- Displays current gestational age in weeks and days
- Most accurate method selection guidance