Pregnancy Due Date Calculator

Calculate your pregnancy due date and get detailed information about your pregnancy journey. Our free calculator supports multiple calculation methods and provides week-by-week development information.

Enter the first day of your last menstrual period
Average length of your menstrual cycle (21-35 days)
Enter the date you conceived (if known)
Enter your known or estimated due date

How It Works

Pregnancy due date calculators use established medical methods to estimate when your baby will arrive. The most common method is based on Naegele's Rule, which adds 280 days (40 weeks) to the first day of your last menstrual period (LMP).

This calculation assumes a 28-day menstrual cycle with ovulation occurring on day 14. If your cycle length differs, the calculator adjusts the due date accordingly. For example, if you have a 32-day cycle, 4 days are added to account for later ovulation.

The three calculation methods available are:

  • Last Menstrual Period (LMP): The most common method, adding 280 days to your LMP date
  • Conception Date: If you know when conception occurred, adds 266 days (38 weeks)
  • Known Due Date: Calculates backwards to determine current pregnancy progress

Remember that only about 4% of babies are born on their exact due date. Most healthy pregnancies deliver within 2 weeks before or after the estimated date.

Frequently Asked Questions

Due date calculators provide estimates based on standard gestational periods. Only about 4% of babies are born on their exact due date. Most healthy pregnancies deliver within 2 weeks before or after the estimated date. Your healthcare provider may adjust your due date based on ultrasound measurements, especially early pregnancy scans which are the most accurate.

Gestational age is calculated from the first day of your last menstrual period and is the standard used in pregnancy. Fetal age (or conceptional age) is calculated from the actual date of conception and is about 2 weeks less than gestational age. Medical providers use gestational age because it's easier to determine accurately.

Yes, your due date may be adjusted based on ultrasound measurements, particularly if performed in the first trimester when measurements are most accurate. An early ultrasound (before 13 weeks) can date a pregnancy within 3-5 days. If there's a significant discrepancy between your LMP date and ultrasound measurements, your provider may change your due date.

If you don't remember your last menstrual period, your healthcare provider will use an early ultrasound to determine gestational age and due date. The ultrasound measures the baby's size to estimate how far along you are. This is also common for those with irregular periods or who conceived while breastfeeding.

Yes, if your menstrual cycle is longer or shorter than the standard 28 days, this affects when ovulation occurs and therefore impacts your due date. For cycles longer than 28 days, your due date would be later; for shorter cycles, it would be earlier. Most calculators can adjust for different cycle lengths.

The American College of Obstetricians and Gynecologists defines full term as 37-42 weeks. However, there are more specific categories: early term (37-38 weeks), full term (39-40 weeks), late term (41 weeks), and post-term (42+ weeks). Babies born at 39-40 weeks have the best outcomes on average.

Conception typically occurs about 14 days after the first day of your last period (for a 28-day cycle). This corresponds to ovulation. If you know the exact conception date (from fertility treatments, for example), your due date is calculated by adding 266 days (38 weeks) from that date.

Pregnancy is divided into three trimesters: First trimester (weeks 1-12), second trimester (weeks 13-26), and third trimester (weeks 27-40). Each trimester is characterized by specific developmental milestones and common pregnancy symptoms. This division helps track development and schedule appropriate prenatal care.

Most healthcare providers recommend scheduling your first prenatal visit between 8-10 weeks of pregnancy. However, if you have a high-risk pregnancy or certain medical conditions, you may need to be seen earlier. This first visit includes confirming the pregnancy, establishing the due date, and beginning prenatal testing.

Going past your due date is common and usually not concerning. Most providers allow pregnancy to continue to 41-42 weeks with increased monitoring. After 42 weeks, risks increase slightly, so induction is typically recommended. Your provider will monitor you more frequently if you go past your due date, checking baby's movements, heart rate, and amniotic fluid levels.
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Popular Due Dates

LMP: January 1, 2025 LMP: March 15, 2025 LMP: June 1, 2025 LMP: September 1, 2025 Conception: February 14, 2025 Conception: May 1, 2025 Due Date: December 25, 2025 Due Date: October 31, 2025

Learn More

  • Pregnancy - Wikipedia

    Comprehensive overview of pregnancy, gestational development, and prenatal care from conception through childbirth.

  • Prenatal Development - Wikipedia

    Detailed information about fetal development stages, from fertilization through the embryonic and fetal periods.

  • Obstetrics - Wikipedia

    Medical field focused on pregnancy, childbirth, and postpartum care, including prenatal testing and delivery methods.

Mathematical Explanation

<h3>Calculation Methods</h3> <p>The pregnancy due date calculator uses these established medical formulas:</p> <ul> <li> <strong>Naegele's Rule (LMP Method)</strong>: Due Date = LMP + 280 days + (Cycle Length - 28 days)<br> This method assumes ovulation occurs 14 days into your cycle. For non-standard cycles, the adjustment accounts for earlier or later ovulation. </li> <li> <strong>Conception Date Method</strong>: Due Date = Conception Date + 266 days<br> This calculation uses 38 weeks (266 days) from conception to birth, which is 2 weeks less than the gestational age method. </li> <li> <strong>Due Date Method</strong>: Works backwards from a known due date to calculate current pregnancy progress and key milestones. </li> </ul> <p><strong>Note</strong>: These calculations provide estimates. Only 4% of babies are born exactly on their due date. Ultrasound measurements may adjust your estimated due date.</p>

Frequently Asked Questions

Due date calculators provide estimates based on standard gestational periods. Only about 4% of babies are born on their exact due date. Most healthy pregnancies deliver within 2 weeks before or after the estimated date. Your healthcare provider may adjust your due date based on ultrasound measurements, especially early pregnancy scans which are the most accurate.

Gestational age is calculated from the first day of your last menstrual period and is the standard used in pregnancy. Fetal age (or conceptional age) is calculated from the actual date of conception and is about 2 weeks less than gestational age. Medical providers use gestational age because it's easier to determine accurately.

Yes, your due date may be adjusted based on ultrasound measurements, particularly if performed in the first trimester when measurements are most accurate. An early ultrasound (before 13 weeks) can date a pregnancy within 3-5 days. If there's a significant discrepancy between your LMP date and ultrasound measurements, your provider may change your due date.

If you don't remember your last menstrual period, your healthcare provider will use an early ultrasound to determine gestational age and due date. The ultrasound measures the baby's size to estimate how far along you are. This is also common for those with irregular periods or who conceived while breastfeeding.

Yes, if your menstrual cycle is longer or shorter than the standard 28 days, this affects when ovulation occurs and therefore impacts your due date. For cycles longer than 28 days, your due date would be later; for shorter cycles, it would be earlier. Most calculators can adjust for different cycle lengths.

Resources & References

Encyclopedia Resources
  • Pregnancy - Wikipedia - Comprehensive overview of pregnancy, gestational development, and prenatal care from conception through childbirth.
  • Prenatal Development - Wikipedia - Detailed information about fetal development stages, from fertilization through the embryonic and fetal periods.
Educational Resources
  • Pregnancy - Wikipedia - Comprehensive overview of pregnancy, gestational development, and prenatal care from conception through childbirth.
  • Prenatal Development - Wikipedia - Detailed information about fetal development stages, from fertilization through the embryonic and fetal periods.