Due Date Calculator

Due Date Calculator - Free Online Pregnancy Due Date Tool

Estimate your baby's due date with our free online Due Date Calculator. Simply enter the first day of your last menstrual period (LMP), and the tool will calculate your estimated delivery date, current pregnancy week, trimester, and days remaining. This calculator uses Naegele's rule, the same method used by healthcare providers worldwide, to give you a reliable estimate of when your baby is expected to arrive.

Knowing your estimated due date is one of the most important pieces of information during pregnancy. It helps you and your healthcare team plan prenatal checkups, prepare for delivery, track fetal development milestones, and arrange maternity or paternity leave. While every pregnancy is unique, the due date provides a valuable reference point for the months ahead.

How to Use

1. Recall the first day of your last menstrual period (LMP). This is the date your most recent period started, not the date it ended.
2. Enter this date in the date picker field.
3. Click "Calculate" to see your results.
4. Review your estimated due date, current pregnancy week, the trimester you are in, and the number of days remaining until your due date.

Understanding the Calculation

• Naegele's Rule: The due date is calculated by adding 280 days (40 weeks) to the first day of the last menstrual period. This is the standard method used by obstetricians and midwives around the world.
• Pregnancy Weeks: Pregnancy is measured from the LMP date, not from conception. Conception typically occurs around week 2, meaning you are technically considered "pregnant" about two weeks before the egg is actually fertilized.
• Trimesters: The first trimester covers weeks 1-12, the second trimester covers weeks 13-27, and the third trimester covers weeks 28-40. Each trimester involves distinct stages of fetal development and different prenatal care focuses.

Important Pregnancy Milestones by Week

• Week 6-8: First heartbeat can be detected via ultrasound.
• Week 12: End of first trimester; risk of miscarriage decreases significantly.
• Week 20: Halfway point; anatomy scan ultrasound is typically performed.
• Week 24: Fetus reaches viability milestone.
• Week 37: Pregnancy is considered "early term"; the baby is nearly fully developed.
• Week 39-40: Full term; the ideal window for delivery.

Frequently Asked Questions

Q. How accurate is the estimated due date?

A. Only about 4-5% of babies are born on their exact due date. The due date is an estimate, and a normal, full-term delivery can occur anytime between 37 and 42 weeks of pregnancy. Most babies arrive within two weeks before or after the estimated due date. An early ultrasound (performed before 12 weeks) can provide a more precise estimate if there is a discrepancy with the LMP-based calculation.

Q. What if I do not remember the exact date of my last period?

A. If you are unsure of your LMP date, enter your best estimate. Your healthcare provider can use an early ultrasound to measure the baby and establish a more accurate due date. The ultrasound measurement of the fetus, particularly in the first trimester, is highly reliable for dating the pregnancy and may be used to adjust the LMP-based estimate.

Q. Does this calculator work for irregular menstrual cycles?

A. This calculator assumes a standard 28-day menstrual cycle with ovulation occurring around day 14. If your cycles are significantly longer or shorter than 28 days, the estimated due date may be off by several days. Women with irregular cycles should discuss their due date with their healthcare provider, who may adjust the estimate based on ultrasound measurements or known ovulation dates. This tool is intended for informational purposes and does not replace professional medical advice.