Pregnancy Due Date Calculator
Estimate your due date from your last menstrual period (LMP) or from a known conception date. See your current weeks pregnant, trimester breakdown, and countdown to birth.
Due date is an estimate based on a 40-week (280-day) pregnancy from LMP. Ultrasound dating is more accurate and may differ by 1–2 weeks.
How is due date calculated?
The standard method for calculating a due date is Naegele's rule: add 280 days (40 weeks) to the first day of the last menstrual period (LMP). This assumes a 28-day menstrual cycle and ovulation on day 14.
If you know your conception date instead, the calculator adds 266 days (38 weeks). This is because pregnancy is counted from LMP, which is typically 14 days before conception.
Only about 4% of babies are born exactly on their due date. Most births occur within two weeks before or after the estimated date.
Pregnancy trimesters
- First trimester (weeks 1–12) — All major organs begin forming. Risk of miscarriage is highest in this period. Most women experience nausea, fatigue, and breast tenderness.
- Second trimester (weeks 13–28) — The foetus grows rapidly and movements become perceptible. Nausea typically eases. Anatomy ultrasound is usually performed around week 20.
- Third trimester (weeks 29–40) — The baby gains weight and prepares for birth. The lungs mature and the baby drops into position. Pre-term birth is defined as delivery before 37 weeks.
Frequently asked questions
Is this calculator a substitute for a doctor's dating scan?
No. An early ultrasound (dating scan) at 8–12 weeks is the most accurate way to confirm gestational age. Ultrasound dating is typically within 3–5 days of the true gestational age, while LMP-based calculation can vary if your cycle length differs from 28 days.
What if my cycle is longer or shorter than 28 days?
Naegele's rule assumes a 28-day cycle with ovulation on day 14. If your cycle is consistently longer (e.g., 35 days), ovulation occurs around day 21, so your due date would be about 7 days later than the standard calculation. Your obstetrician will typically adjust the due date based on your first ultrasound.
When is a baby considered full term?
Full term is defined as 39–40 weeks of gestation. Early term is 37–38 weeks, late term is 41 weeks, and post-term is 42 weeks or beyond. Births before 37 weeks are considered pre-term. Gestational age at birth is one of the strongest predictors of neonatal health outcomes.
