Wondering when your baby might arrive? Our due date calculator estimates your baby’s due date using the first day of your last menstrual period, your average cycle length, and whether this is your first pregnancy.
Most healthcare providers use your last menstrual period to estimate your due date, then confirm or adjust it with an early ultrasound. This calculator gives you a helpful starting point as you plan for pregnancy and your first prenatal appointments.
Enter your information above to estimate your baby’s due date.
Your results are an estimate based on the information you provide and should not replace guidance from your healthcare provider.
A pregnancy due date calculator estimates when your baby is likely to be born based on the first day of your last menstrual period. Some calculators, including ours, also consider your average cycle length and pregnancy history to provide a more personalized estimate.1
Don’t Know the Date of Your Last Period?
If you’re unsure of the exact start date of your last menstrual period (LMP), you’re not alone. Enter your best estimate if you’re unsure. Your healthcare provider can confirm or adjust your estimated due date (EDD) with an early ultrasound or at a prenatal appointment.
How Does the Due Date Calculator Work?
Healthcare providers use several methods to estimate your due date.1 The most common method begins with the first day of your last menstrual period (LMP), which most healthcare providers use to estimate your due date.
Our due date calculator uses two methods: Naegele’s Rule and the Woods Method, also known as Nichols’ Rule. Naegele’s Rule is the standard 40-week calculation most doctors and midwives use. However, it assumes a 28-day menstrual cycle and does not account for your average cycle length or whether you’ve given birth before, which can make the estimate less accurate for some pregnancies.1
That’s why we also include Nichols’ Rule. It factors in your average cycle length and whether you’ve given birth before. Together, these two calculations give you the due date your provider is likely using and a second estimate that may better reflect your individual pregnancy.
Ultrasound Confirmation of Your Due Date
After estimating your due date from the first day of your last menstrual period, your healthcare provider may confirm it with an early prenatal ultrasound. According to ACOG, “Ultrasound measurement of the embryo or fetus in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate method to establish or confirm gestational age.” ACOG also provides guidelines for confirming your due date using both ultrasound findings and menstrual dating.5
Can Your Due Date Change During Pregnancy?
Once your due date is confirmed by ultrasound, it usually does not change. First-trimester ultrasounds are generally more accurate than menstrual-based estimates, especially if you have irregular cycles. Your provider will follow ACOG’s guidelines to determine your pregnancy’s timeline, using menstrual calculations first and confirming them with an ultrasound.5
Menstrual dating can be less reliable, especially if you have irregular cycles, because it’s harder to pinpoint when ovulation or conception occurred.
Keep in mind: Conception doesn’t always happen on the day of intercourse. Sperm can survive in the reproductive tract for up to five days.2 This means conception may occur on the day you ovulate, even if intercourse occurred several days earlier. Conception takes place when an egg is released and fertilized, not necessarily the day of intercourse.
Will You Go Into Labor on Your Due Date?
Despite the name, your due date is only an estimate. Only about 5% of women deliver on their exact due date.3
Most expectant moms, especially those carrying a single baby, can expect to go into labor sometime within the two weeks before or after their due date. If you’re pregnant with multiples, it’s common to deliver even earlier, typically about two weeks ahead of schedule.
On average, first-time moms tend to deliver around eight days past their due date.4 While your due date is a helpful estimate, every pregnancy unfolds on its own timeline.
