Complete Pregnancy Due Date Calculator Guide 2025

The moment you discover you're expecting, one of the first questions that comes up is: "When will I meet my baby?" While only a small percentage of babies are born exactly on their calculated due date, having an estimated arrival window is a helpful reference point for medical tracking and personal preparation.

Our Pregnancy Due Date Calculator uses the first day of your last menstrual period (LMP) and your average cycle length to estimate your due date (EDD), current gestational age, and trimester. It's completely free, private (calculations happen in your browser), and requires no sign-up.

Did You Know? Pregnancy is traditionally calculated as 40 weeks (280 days) starting from the first day of your last period, even though conception typically happens about two weeks later.

How This Calculator Estimates Your Due Date

This calculator uses Naegele's Rule, adjusted for your specific cycle length. The standard version of this rule adds 280 days (40 weeks) to the first day of your last period; this calculator further adjusts the result based on how far your entered cycle length differs from the standard 28 days.

EDD = LMP + 280 Days + (Cycle Length − 28)

Example: For a 28-day cycle, EDD = LMP + 280 days exactly. For a 32-day cycle, EDD = LMP + 284 days.

How to Use This Calculator:

Enter the First Day of Your Last Period (LMP).
Enter Your Average Cycle Length: Default is 28 days; adjust between 20–45 days if yours differs.
Review Results: See your Estimated Due Date, current weeks/days pregnant, days remaining, and current trimester.

Note on Method: This calculator estimates your due date from your LMP and cycle length only. If you know your exact conception date instead (for example, from IVF or ovulation tracking), your healthcare provider can calculate your due date directly from that date, which may give a slightly different estimate than the LMP-based method.

Other Ways Due Dates Are Estimated

Ultrasound Dating

In early pregnancy, a sonogram measuring the "crown-rump length" of the embryo is often considered the most accurate way to date a pregnancy, especially for people with irregular cycles or an uncertain LMP.

Something to Keep in Mind: Your due date is really the middle of a "due window." A full-term pregnancy is generally considered anywhere between 37 and 42 weeks, so treat the date as an estimate rather than a fixed appointment.

Irregular Cycles: If your periods are not regular, calendar-based calculations like this one may be less precise. Your doctor will likely use an early dating ultrasound to give you the most reliable estimate in that case.

General Pregnancy Timeline

Stage	Typical Weeks
First Trimester	Weeks 1 – 13
Second Trimester	Weeks 14 – 26
Third Trimester	Weeks 27 – Birth
Full Term	Weeks 37 – 42

This matches the trimester ranges this calculator uses to determine your current trimester.

Common Mistakes to Avoid

1. Treating the Due Date as a Fixed Deadline

Since full-term birth spans a five-week window (37–42 weeks), it's more realistic to think in terms of a due month or window rather than a single exact day.

2. Not Adjusting for an Irregular Cycle

If your cycle is consistently longer or shorter than 28 days, entering your actual average cycle length gives a more accurate estimate than leaving the default.

3. Relying on LMP Alone With an Uncertain Date

If you're unsure of your exact LMP date, an early ultrasound from your healthcare provider will generally give a more reliable estimate than a calendar-based calculation.

Medical Disclaimer: This calculator is for informational and educational purposes only. It is not a medical diagnosis. Always consult with your OB-GYN or a qualified healthcare provider for prenatal care and to confirm your official due date.

Conclusion

Your estimated due date is a helpful planning reference, but it's just that — an estimate. Use the calculator above to get your starting point, and rely on your healthcare provider's ongoing prenatal care, including ultrasounds, for the most accurate and personalized picture of your pregnancy's progress.

Pregnancy & Arrival: Frequently Asked Questions

How accurate is the due date calculator?

It provides a very good estimate based on biological averages. However, only 1 in 20 women gives birth on their actual due date. It is better to view it as a "due month."

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

Don't worry! In such cases, your healthcare provider will perform an ultrasound to measure the baby's size, which is highly accurate for dating in the first trimester.

Can my due date change?

Yes. If an early ultrasound shows the baby is significantly larger or smaller than expected based on your LMP, your doctor may adjust your official "due date."

Does cycle length matter?

Absolutely. Our calculator allows you to adjust your cycle length. If you have a 35-day cycle instead of 28, you likely ovulated later, which moves your due date back about a week.

Can I calculate my due date from my conception date instead of LMP?

This calculator only accepts your last period date and cycle length. If you know your exact conception date, your healthcare provider can calculate your due date directly from it (typically conception date + 266 days), which may differ slightly from the LMP-based estimate.

Pregnancy Due Date

Select your LMP to see the magic!