Pregnancy Due Date Calculator
Estimate your baby's due date from the first day of your last period. See how many weeks along you are, your current trimester, a countdown to your due date, and your estimated conception date.
How to use it
Enter the first day of your last menstrual period and, if you know it, your average cycle length. The calculator uses Naegele's rule — last period plus 280 days — adjusting for cycle length, and shows how far along you are today.
This is an estimate: only about 1 in 20 babies arrive on the exact due date, and most arrive within a week or two either side. An ultrasound dating scan, especially in the first trimester, gives a more accurate date.
Frequently asked questions
How is my due date calculated?
By Naegele's rule: 280 days (40 weeks) are added to the first day of your last menstrual period. If your cycle is longer or shorter than 28 days, the calculator adjusts the date for when you likely ovulated.
How accurate is a due date?
It's an estimate. Only around 4–5% of babies are born on their exact due date; most arrive within two weeks either side. An early ultrasound dating scan is the most accurate way to date a pregnancy.
What if I don't know my last period date?
The last-period method needs that date. If you're unsure, or your cycles are irregular, an ultrasound dating scan from your healthcare provider is the best way to estimate your due date.
BriskToolbox provides estimates for general information only and is not medical advice. Talk to a healthcare professional about your individual health.