Due Date Calculator
Enter the first day of your last menstrual period to estimate your due date and how far along you are.
About this calculator
This due date calculator uses Naegele's rule — the standard obstetric estimate of adding 280 days (40 weeks) to the first day of the last menstrual period (LMP) — to project a due date.
It also shows how far along the pregnancy is today and an estimated conception date. These are population averages: your care provider's ultrasound dating scan, especially in the first trimester, is more precise for an individual pregnancy.
How it works
Enter the first day of your last period
This is the standard reference point used in obstetric dating.
Calculate
The calculator adds 280 days to project the estimated due date.
Review the estimate
See the due date, current gestation in weeks and days, trimester, and estimated conception date.
Frequently asked questions
How accurate is a due date based on LMP?
Only about 1 in 20 babies arrive exactly on the estimated due date — it's a statistical midpoint, and a first-trimester ultrasound is generally considered more accurate.
What if my cycle isn't a regular 28 days?
Naegele's rule assumes a 28-day cycle with ovulation on day 14; if your cycles run longer or shorter, the estimate may be off by several days — your provider can adjust for this.
Is this a substitute for medical care?
No. This tool is for general information only — always confirm dates and monitor the pregnancy with a qualified healthcare provider.