Health
Pregnancy due date calculator
Enter the first day of the last menstrual period and the usual cycle length. The estimate uses Naegele's rule, 280 days from that date, with a common adjustment for cycle length.
What this means
- The estimated due date is May 8, 2027.
- Due dates are estimates. Many births happen in the weeks around the date, not on it.
- A clinician may adjust the date after an early ultrasound.
What if
About this calculator
What this calculator does
It adds 280 days (40 weeks) to the first day of the last menstrual period, then applies a common adjustment: it shifts the date by how much the cycle differs from 28 days. ACOG notes that the most accurate dating uses an early ultrasound, and your care team may set a different date.
How it is calculated
due date = last period + 280 days + (cycle length - 28), the cycle adjustment
conception estimate = last period + 14 days + (cycle length - 28)
weeks along = days since last period / 7
How to read the result
Pregnancy is counted from the last period, about two weeks before conception. That is why weeks along is higher than the time since conception.
Trimesters
This page uses the common split: first trimester through week 13, second from week 14 through week 27, and third from week 28.
Sources and method
Last menstrual period plus 280 days (ACOG convention), with a common cycle-length adjustment.
Questions
What is Naegele's rule?
A standard method that adds 280 days to the first day of the last period to estimate the due date.
Why does cycle length change the date?
Ovulation tends to happen later in longer cycles, so the estimate moves later too.
How accurate is the due date?
It is an estimate. An early ultrasound may give a different date, and your clinician's date takes priority.
Why is the as-of date not today automatically?
Pages are built ahead of time so they load fast and keep shareable links stable. Set the date to today.