Introduction
The Due Date Calculator helps you figure out when your baby is likely to be born. The average pregnancy lasts 280 days, or 40 weeks, from the first day of your last menstrual period.3 By entering this date, our calculator estimates your expected due date so you can plan ahead and track your pregnancy week by week. Keep in mind that a due date is an estimate; ACOG calls a pregnancy of 41 to 42 weeks late term and one beyond 42 weeks postterm.3 Your doctor or midwife may adjust your due date based on ultrasound results or other factors. This tool gives you a helpful starting point to understand your pregnancy timeline.
How to Use Our Due Date Calculator
Enter details about your pregnancy using one of four methods, and this calculator will estimate your due date, show your current gestational age, and display key milestones throughout your pregnancy.
Calculation Method: Choose how you want to calculate your due date. You can pick from Last Menstrual Period (LMP), Conception Date, IVF Transfer Date, or Ultrasound Date. The fields below will change based on your choice.
First Day of Last Period: If using the LMP method, enter the first day of your most recent menstrual period. This is the most common way doctors estimate a due date.
Average Cycle Length: Enter the typical number of days in your menstrual cycle. The standard is 28 days. If your cycle is longer or shorter, the calculator adjusts your due date to account for the difference.
Conception Date: If you know the exact date you conceived, select the Conception Date method and enter that date. The calculator adds 266 days to find your due date.
Embryo Transfer Date: If you used IVF, select the IVF Transfer Date method and enter the date your embryo was transferred.
Transfer Type: Choose whether your IVF transfer was a Day 3 or Day 5 embryo. A Day 3 transfer adds 263 days and a Day 5 transfer adds 261 days to calculate your due date.
Ultrasound Date: If using the Ultrasound method, enter the date your ultrasound was performed.1 Ultrasound in the first trimester, up to and including 13 weeks and 6 days, is the most accurate method to establish or confirm gestational age.1
Gestational Age at Ultrasound: Enter the number of weeks and days your doctor said the baby measured at your ultrasound. The calculator uses this age along with the ultrasound date to work backward and find your due date.
Once you have filled in your information, click Calculate Due Date to see your estimated due date, a countdown of days remaining, trimester progress, key pregnancy dates, milestones, and a week-by-week timeline. Click Reset to clear your entries and start over.
How to Calculate Your Due Date
A due date calculator estimates the day your baby is most likely to be born. Most pregnancies last about 40 weeks, or 280 days, counted from the first day of your last menstrual period (LMP). This date is also called the estimated date of delivery (EDD). Knowing your due date helps you and your doctor plan prenatal care, schedule important tests, and prepare for your baby's arrival.
Methods Used to Calculate a Due Date
There are several ways to figure out when your baby is due. The most common method uses the first day of your last menstrual period (LMP). The calculator adds 280 days to that date, then adjusts if your cycle is longer or shorter than the standard 28 days. For example, if your cycle is 32 days, your due date shifts forward by 4 days because ovulation likely happened later.1
If you know your conception date, the calculation adds 266 days from that day instead. This works well for people who tracked ovulation closely. For those who used in vitro fertilization (IVF), the due date is based on the embryo transfer date. A Day 3 embryo transfer adds 263 days, while a Day 5 blastocyst transfer adds 261 days, since the embryo is two days more developed.
An ultrasound can also be used to estimate your due date.1 Your doctor measures the baby's size and tells you the gestational age in weeks and days. The calculator uses this information to work backward and find when your pregnancy started, then counts forward to 40 weeks. ACOG calls first-trimester ultrasound, up to and including 13 weeks and 6 days, the most accurate method to establish or confirm gestational age.1
What the Trimesters Mean
Pregnancy is divided into three trimesters. ACOG defines the first trimester as the first day of the last period to 13 weeks and 6 days, the second trimester as 14 weeks and 0 days to 27 weeks and 6 days, and the third trimester as 28 weeks and 0 days onward.2 In the first trimester the baby's organs begin to form, and many women experience morning sickness and fatigue. In the second, most women feel more energetic and the baby grows quickly; an anatomy scan is usually done around weeks 18 to 22. In the third, the baby gains weight rapidly and doctor visits become more frequent.
Key Pregnancy Milestones
Several milestones happen throughout pregnancy. Week 20 marks the halfway point, and week 24 is commonly treated as the viability milestone, meaning the baby has a chance of surviving if born early. ACOG says labor induction may be recommended once a pregnancy reaches 41 weeks.3
How Accurate Is a Due Date?
A due date is an estimate, not a guarantee, and few babies arrive on the day itself. ACOG calls a pregnancy of 41 to 42 weeks late term and one beyond 42 weeks postterm.3 Your doctor may adjust your due date from an early ultrasound: ACOG advises changing the date when ultrasound before 14 weeks differs from the LMP date by more than 7 days.1
Important Things to Keep in Mind
This calculator provides an estimate for educational purposes only. It does not replace medical advice. Always confirm your due date with your healthcare provider, who can use physical exams and ultrasound measurements for the most accurate assessment. If your menstrual cycle is irregular, or if you are unsure about dates, an early ultrasound is the best way to determine gestational age. Talk to your doctor about your specific prenatal care schedule, recommended screenings, and any concerns you may have throughout your pregnancy. During pregnancy, staying on top of your nutrition is important to meet the increased nutritional demands of each trimester, and getting enough rest matters as your body works harder to support your growing baby. Prioritizing safe caffeine limits is also a common concern during pregnancy that is worth discussing with your provider.