What is a pregnancy due date calculator?
A pregnancy due date calculator estimates your expected delivery date (EDD) based on your last menstrual period, conception date, or ultrasound measurements. The due date is calculated as 40 weeks (280 days) from the first day of your last menstrual period, which is the standard method used by healthcare providers. This calculator helps expectant parents plan for their baby's arrival and track pregnancy progress.
Select a calculation method (LMP, conception date, or ultrasound), enter the required date or measurements, then click Get result to see your estimated due date and current weeks of pregnancy. No sign-up required. Use it for planning, but remember that due dates are estimates—most babies are born within 2 weeks before or after the due date.
How to use this pregnancy due date calculator
Choose your calculation method: Last Menstrual Period (most common—enter the first day of your last period), Conception Date (if you know the exact date), or Ultrasound Measurement (enter gestational age from ultrasound). Enter the required information, then click Get result to see your estimated due date and how many weeks pregnant you are. The LMP method is most accurate if you have regular 28-day cycles. If your cycles are longer or irregular, conception date or ultrasound may be more accurate.
Understanding pregnancy due dates
Pregnancy is calculated as 40 weeks (280 days) from the first day of the last menstrual period, even though conception typically occurs about 2 weeks later. This standard accounts for the fact that LMP is easier to track than conception. The due date is an estimate—only about 5% of babies are born exactly on their due date. Most full-term babies (37-42 weeks) are born within 2 weeks before or after. The calculator shows your estimated due date and current weeks of pregnancy based on today's date.
Calculation methods explained
LMP Method: Most common, used by healthcare providers. Adds 280 days (40 weeks) to the first day of your last period. Assumes a 28-day cycle with ovulation on day 14. Conception Date Method: Adds 266 days (38 weeks) from conception date. More accurate if you know the exact conception date, but less commonly used because conception date is harder to determine. Ultrasound Method: Uses gestational age from ultrasound measurements. Most accurate in early pregnancy (first trimester). Later ultrasounds may be less accurate due to natural variation in fetal size.
Pregnancy timeline and trimesters
Pregnancy is divided into three trimesters: First trimester (weeks 1-12): Early development, morning sickness common. Second trimester (weeks 13-27): Baby grows rapidly, mother usually feels better. Third trimester (weeks 28-40): Final growth, preparation for birth. Full-term pregnancy is 37-42 weeks. Babies born before 37 weeks are premature, after 42 weeks are post-term. The calculator shows your current week of pregnancy, helping you understand which trimester you're in and what to expect.
When to consult healthcare providers
This calculator provides estimates for planning and information. Always confirm your due date with your healthcare provider, who will use clinical methods (LMP, physical exam, ultrasound) to determine the most accurate due date. Your provider may adjust the due date based on early ultrasound measurements, especially if your cycles are irregular. Regular prenatal care is essential for monitoring pregnancy progress and ensuring both mother and baby's health.
Tips for accurate calculation
Use the LMP method if you have regular cycles and remember the first day of your last period accurately. If your cycles are longer than 28 days, add the extra days to the due date. For example, if your cycle is 35 days, add 7 days to the standard calculation. If you've had an early ultrasound (before 14 weeks), that measurement is most accurate for determining due date. Your healthcare provider will use the most accurate method based on your individual situation.
Summary
This pregnancy due date calculator estimates your expected delivery date using LMP, conception date, or ultrasound measurements. Enter your information and click Get result to see your due date and current weeks of pregnancy. It's free, works in your browser, and requires no account. Use it for planning and information, but always confirm with your healthcare provider, who will determine the most accurate due date based on clinical assessment. Remember that due dates are estimates—most babies arrive within 2 weeks of the due date.