Due Date Calculator

Using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). Only about 5% of babies are born on their exact due date — most arrive within 2 weeks before or after.

If you know your conception date, add 266 days (38 weeks). Your doctor can also estimate due date from an early ultrasound, which is most accurate in the first trimester.

First trimester: weeks 1-12 (major organ development). Second trimester: weeks 13-26 (rapid growth, movement felt). Third trimester: weeks 27-40 (weight gain, preparation for birth).

Using the Due Date Calculator is simple: visit the tool page, enter your data or input into the provided fields, and get instant results. Follow the controls on the page. Some functions require sign-in or a paid plan; see Pricing for limits.

The Free plan includes 10 tool uses per day. Some features require an account or a paid plan. Check the controls on the tool page and Pricing for the applicable limits.

Yes, the Due Date Calculator is fully responsive and works perfectly on smartphones, tablets, and desktop computers. Simply open NexTool in your mobile browser and navigate to the tool — no app download required.