Looking for a pregnancy due date calculator from last period? This free tool gives you due date, conception date, current week and trimester. Just enter your numbers and press Calculate — results are instant.
A pregnancy is counted as 40 weeks from the first day of the last menstrual period — this is Naegele's rule, the standard doctors use. Add 280 days to that date to get the estimated due date, and adjust by the difference if your cycle is longer or shorter than 28 days. Conception is estimated at about 14 days after the last period. The due date is an estimate: most babies arrive within a couple of weeks either side of it.
Example: First day of last period 1 August 2026 · Average cycle 28 days
Estimated Due Date: Sat May 08 2027
The standard way to estimate a due date: add 280 days (40 weeks) to the first day of the last period. It assumes a 28-day cycle, so the calculator adjusts when your cycle is longer or shorter.
Yes, and the calculator handles it: the due date shifts by your cycle length minus 28 days. A 35-day cycle moves the due date about a week later than a 28-day cycle would.
Usually yes, especially an early scan. Ultrasound measures the baby directly, while the LMP method assumes ovulation happened on day 14, which is not true for everyone.
It is an estimate. Most babies arrive within a couple of weeks either side of the due date, and only a small share arrive on the exact day. The date is mainly used to plan care and check growth.