How to Calculate Your Due Date

Quick Answer

Quick Answer: Most pregnancies are estimated at 280 days (40 weeks) from the first day of your last menstrual period (LMP). If your LMP was January 1, your due date is roughly October 8. Use our Pregnancy Due Date Calculator.

How due dates are calculated

Healthcare providers commonly use Naegele's rule: LMP + 1 year − 3 months + 7 days (or simply add 280 days). Only about 5% of babies arrive on the exact due date—it's an estimate, not a deadline.

Ultrasound vs LMP

Early ultrasounds (especially in the first trimester) can refine the due date if your cycles are irregular. Always follow guidance from your prenatal care team.

Try It Yourself

Enter your LMP in our free Pregnancy Due Date Calculator for an instant estimate with weeks remaining.

Frequently Asked Questions

How accurate is a due date from LMP?

It's a good starting estimate for regular 28-day cycles. Irregular periods or late ovulation can shift the true date.

Can I use conception date instead?

Yes—conception-based estimates typically add about 266 days from conception. Your clinician may adjust based on ultrasound.

Is this medical advice?

No. This article and tool are informational only. See your healthcare provider for prenatal care.

Medical Disclaimer: The tools and content on LifeToolbox are for informational purposes only and are not intended as medical advice, diagnosis, or treatment.