Due Date Calculator

Free due date calculator with two modes: pregnancy due date (Naegele's rule from last menstrual period) and project deadline calculator. View trimester timeline, week-by-week development, key milestones, and days remaining.

First Day of Last Menstrual Period

Enter a date above to calculate your estimated due date and pregnancy timeline.

Medical Disclaimer

This calculator provides an estimate only based on Naegele's Rule (LMP + 280 days). Only about 5% of babies are born on their exact due date.

This tool is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider for accurate pregnancy dating.

How It Works

Naegele's Rule: The due date is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP).

Conception Date Method: If you know the conception date, the calculator subtracts 14 days to estimate the equivalent LMP, then applies Naegele's Rule.

Trimesters: First trimester spans weeks 1-13, second trimester weeks 14-27, and third trimester weeks 28-40.

How to Use Due Date Calculator

1Choose mode: Pregnancy or Project.
2Enter your last period date or project start date.
3View the calculated due date and timeline.
4Check milestones and week-by-week information.

Frequently Asked Questions

How is the pregnancy due date calculated?▾

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.

What if I don't know my last period date?▾

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.

What are the trimesters?▾

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).

About Due Date Calculator

NexTool's Due Date Calculator is completely free to use with no sign-up required. Your data is processed directly in your browser and never sent to our servers, ensuring complete privacy and instant results.