Pregnancy Due Date Calculator
Estimate your due date and how far along you are, from your last period.
How it works
Based on Naegele's rule: due date ≈ last period + 280 days. This is an estimate — only an ultrasound and your doctor can confirm dates.
How it works
This calculator estimates your due date and how far along you are from the first day of your last menstrual period (LMP). It follows Naegele's rule: pregnancy is counted as about 280 days (40 weeks) from that first day. Counting from the LMP rather than conception is the medical standard, because the LMP date is far easier to know precisely. It does mean the first couple of 'pregnancy weeks' technically occur before conception — a quirk of the convention, not an error. Only about 4 in 100 babies arrive exactly on the due date; most births fall within roughly two weeks either side. An early ultrasound gives a more precise date, especially if your cycle is irregular, so treat this as a well-founded estimate.
Advertisement
Frequently asked questions
How is my due date calculated?
It's estimated as 280 days (40 weeks) from the first day of your last menstrual period (Naegele's rule).
Is the due date exact?
No — it's an estimate. Only about 1 in 20 babies arrive on the exact due date; most are born within two weeks before or after.
How accurate is the due date?
It is an estimate — only about 5% of babies are born on the exact date, and most arrive within about two weeks either side. An early ultrasound refines it.
Advertisement