Due Date Calculator

What is a Due Date Calculator?

A due date calculator estimates when your baby is likely to be born. Pregnancy lasts about 40 weeks on average, and the due date is usually calculated from the first day of the last menstrual period. This tool accepts either that date or the conception date, depending on what information you have, and returns the estimated due date along with your current week of pregnancy and days remaining.

The due date is one of the first pieces of information a healthcare team works out, because it anchors the entire timeline of prenatal care. Tests, scans, and milestones are scheduled relative to it. Knowing your due date early also helps you plan leave from work, arrange support, and follow week-by-week pregnancy guidance with confidence.

How to Use the Due Date Calculator

Using the calculator takes just a moment. Choose which date you know, enter it, and get your estimate.

1. Choose “Last menstrual period” or “Conception date” based on the information you have.
2. Enter the date in the date field.
3. Click “Calculate Due Date” to see the estimated due date and current week.
4. Note the days remaining and share the date with your care provider to confirm.

How the Due Date Is Calculated

The calculation depends on the date you provide:

• From LMP: add 280 days (40 weeks) to the first day of the last period.
• From conception: add 266 days (38 weeks) to the conception date.

The 14-day difference between these two methods reflects the typical gap between the first day of a period and conception in a standard 28-day cycle. Both approaches are widely used in maternity care, and they should produce roughly the same due date.

Understanding the Current Week

Pregnancy is counted from the LMP, so the current week shown tells you how far along you are in the standard 40-week count. Knowing your week lets you follow development guides and understand what to expect at each stage. Because conception usually occurs about two weeks after the LMP, the first two weeks of the count are before you were actually pregnant, which is a normal part of how healthcare providers measure pregnancy.

What to Know About Accuracy

The due date is an estimate, not a guarantee. Only about 1 in 20 babies arrive exactly on their due date, and most are born within two weeks before or after it. Doctors often adjust the date after an early ultrasound, which measures the baby to estimate gestational age more precisely. Regular cycles of 28 days give the most accurate calendar-based estimates, while irregular cycles make them less reliable.

What This Calculator Tells You

In addition to the due date, the tool shows your current week of pregnancy and the number of days remaining. These figures help you track progress between appointments, plan for the months ahead, and communicate clearly with your healthcare team about where you are in your pregnancy.

Worked Example: From Last Period to Due Date

Let us follow a complete example so the output makes sense. Suppose the first day of your last menstrual period was June 1, 2026.

• Due date: Adding 280 days gives a due date around March 8, 2027.
• Current week: If today is August 7, 2026, about 67 days have passed, which puts you in week 10 of the pregnancy.
• Days remaining: Roughly 213 days remain until the estimated due date.

If instead you knew the conception date and entered June 15, 2026, the calculator adds 266 days and arrives at a very similar due date. The small difference between the two methods reflects the assumptions built into each, and your care provider can help reconcile them if they differ.

Pregnancy Weeks and Trimesters

Pregnancy is measured in weeks from the LMP, not in months, which is why a term pregnancy is called 40 weeks even though that is about nine calendar months. Understanding the timeline helps you make sense of the current week the calculator shows:

• First trimester: Weeks 1 to 12, the period of early development and typically the first ultrasound window.
• Second trimester: Weeks 13 to 27, when many prenatal tests and the anatomy scan are scheduled.
• Third trimester: Weeks 28 to 40, when growth accelerates and preparations for delivery ramp up.

Because weeks are counted from the LMP, weeks 1 and 2 fall before conception actually occurs. This is a standard convention in maternity care rather than a mistake in the count.

Why the Date Often Changes After an Ultrasound

Calendar estimates assume a regular 28-day cycle and ovulation at day 14, which does not fit everyone. An early ultrasound offers a different kind of evidence:

• The ultrasound measures the embryo or fetus to estimate gestational age from physical size, which is less dependent on cycle regularity.
• In the first trimester the dating is most accurate, since growth is relatively uniform early on and differences between babies are small.
• If the ultrasound estimate differs from the LMP estimate by a week or more, providers often adjust the due date to the scan-based date.

This is why many clinics describe the due date as provisional until after the first scan, and why it is wise to confirm rather than rely on the calendar figure alone.

Planning for the Due Date Window

A due date is the center of a range, not a single guaranteed day. Around 80% of births happen between two weeks before and two weeks after the estimated date. Practical planning should reflect that:

• Prepare your maternity leave and work handover to start a little before the due date and remain flexible afterwards.
• Pack the hospital bag and arrange transport a few weeks early, since labor can start before the date.
• Keep plans light around the window, especially travel, so you are not far from home when labor begins.
• Discuss late-term options with your provider, since monitoring may intensify if the pregnancy continues past 41 weeks.

Important Notes

• The due date is an estimate, not a guarantee.
• Only about 1 in 20 babies arrive exactly on their due date.
• Doctors often adjust the date after an early ultrasound.
• Regular cycles of 28 days give the most accurate estimates.
• Confirm your due date with your healthcare provider.

Why Use This Due Date Calculator?

• Works with either LMP or conception date
• Shows due date, current week, and days remaining
• Instant results with no signup
• Free and unlimited use
• No data is ever uploaded
• Works on any device with a browser