Due Date Calculator

How the due date is calculated

Naegele's rule — first day of last menstrual period (LMP) + 280 days = estimated due date. This assumes a regular 28-day cycle with ovulation around day 14. If you know the conception date, the tool uses date + 266 days.

Trimester breakdown

• First trimester — weeks 1-12. Most rapid development; biggest risk window.
• Second trimester — weeks 13-26. The "easier" trimester for most; energy returns.
• Third trimester — weeks 27-40+. Final growth phase; preparation for birth.

Privacy

All calculation happens in your browser. The dates you enter are not uploaded anywhere.

Not medical advice. Only an ultrasound dating scan gives a clinically accurate due date. Just 4-5% of babies are actually born on their estimated date — most arrive within 2 weeks before or after.