Wondering when your baby might arrive? Our due date calculator helps you estimate your baby’s birthday based on the first day of your last menstrual period. It’s the same approach most healthcare providers use to determine an expected due date. Whether you’re tracking your early symptoms or planning ahead, this simple tool offers both standard and personalized estimates so you can feel more confident as you prepare for your pregnancy journey.
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. Try entering your best estimate into the due date calculator for now. Your healthcare provider can confirm or adjust your estimated due date with an early ultrasound or during future prenatal appointments.
How Do We Calculate Your Baby’s Due Date?
There are a few different ways to estimate your due date.1 The most common method begins with the first day of your last menstrual period (LMP), which is how most healthcare providers determine your estimated due date (EDD).
Our due date calculator uses two approaches: Naegele’s Rule and the Woods Method, also known as Nichols’ Rule. Why provide both? Naegele’s Rule is the standard 40-week calculation most doctors and midwives use. However, it assumes a 28-day cycle and doesn’t consider whether this is your first pregnancy or your fifth, which can make the result less accurate.1
That’s why we also include the Nichols’ Rule. It factors in your average cycle length and whether you’ve given birth before. This way, you’ll get two helpful perspectives: the EDD your provider is likely using (Naegele’s Rule), and a second date that might more realistically reflect when your baby could arrive (Nichols’ Rule).
Ultrasound Confirmation of Due Date in Early Pregnancy
After estimating your due date using the first day of your last menstrual period, it’s important to 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 detailed guidelines for verifying your estimated due date using both ultrasound findings and menstrual dating.5
Can Your Due Date Change During Pregnancy?
Once your estimated due date (EDD) is confirmed by ultrasound, it typically won’t change. Ultrasounds, particularly in the first trimester, are typically more reliable than menstrual-based estimates, especially for those with 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.
Note: 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 you may conceive 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 estimated due date is just that — an estimate. In fact, 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 the due date offers a helpful guide, every pregnancy unfolds on its own timeline.
