Due Date Calculator
Estimate your due date and see how far along you are today, with your trimester dates and week-by-week milestones. Choose the method that fits your pregnancy.
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Only about 4% of babies arrive on their due date - most come within two weeks either side.
How the due date is calculated
The classic method (Naegele's rule) counts 280 days (40 weeks) from the first day of your last period, assuming a 28-day cycle. We adjust for your actual cycle length:
Due date = last period + 280 days + (cycle length - 28)
From conception: + 266 days
IVF Day-5 transfer: + 261 days · Day-3: + 263 days
Your gestational age today is measured from that effective last-period date. Trimesters follow ACOG: first is weeks 0 to 13+6, second 14 to 27+6, third 28 weeks to birth.
Source: Naegele's rule; ACOG definitions of term and trimesters.
Frequently asked questions
How is a due date calculated?
The standard method (Naegele's rule) adds 280 days to the first day of your last menstrual period, assuming a 28-day cycle. We adjust for your cycle length, or use 266 days from conception.
How accurate is a due date?
Only about 4 percent of babies arrive on their exact due date. Most are born within two weeks either side. An early ultrasound (dating scan) is more accurate than LMP alone.
LMP vs conception vs IVF, which should I use?
Use conception or IVF transfer dates if you know them, as they remove cycle-length guesswork. A Day-5 embryo transfer adds 261 days; a Day-3 transfer adds 263 days.
When do the trimesters change?
First trimester is weeks 0 to 13 and 6 days, second is 14 to 27 and 6 days, and third is 28 weeks to birth.
What does full term mean?
Early term is 37 to 38 weeks, full term is 39 to 40 weeks, and post-term is 42 weeks and beyond.
Medical disclaimer: This calculator is for general information and education only. It is an estimate, not medical advice, diagnosis or treatment. Always talk to your doctor or midwife about your health and any decisions.