How to Accurately Calculate Your Pregnancy Due Date (Even With Irregular Periods)

Wondering when your baby is due? Whether your menstrual cycle is regular or not, knowing how to calculate your due date is one of the first and most important steps in your pregnancy journey.

💡 Why Knowing Your Due Date Matters

Your due date helps track fetal development, schedule ultrasounds, and plan prenatal care. While only about 5% of babies are born on their exact due date, it’s still a vital estimate for both you and your doctor.

🧮 How Due Dates Are Typically Calculated

The most common method is Naegele’s Rule, which adds 280 days (or 40 weeks) to the first day of your last menstrual period (LMP).

For example, if your LMP was January 1, 2025, your estimated due date would be around October 8, 2025.

Try our free calculator here: Due Date Calculator

🤔 What If You Have Irregular Periods?

If your cycles are irregular, don’t worry. You can:

• Use the date of conception (if known)
• Use ovulation tracking (via basal temperature or LH tests)
• Get an early ultrasound to measure fetal size and estimate the gestational age

📱 Use an Online Due Date Calculator

We’ve built a simple, fast, and mobile-friendly due date calculator you can use anytime — completely free.

🔄 Can Your Due Date Change?

Yes. Doctors may adjust it based on early ultrasound measurements. This is normal and usually results in only a slight difference (a few days).

✨ Key Takeaways

• Use the first day of your last period for an estimate
• 280 days (or 40 weeks) is the standard calculation
• Early ultrasounds are most accurate in the first trimester
• Use our free tool to get instant results

Want to know your due date? Try our tool now: DueDateNow