Pregnancy Calculator

Most pregnancies last about 40 weeks from the first day of your last menstrual period. Enter your dates into the pregnancy calculator above to estimate your due date, find out how far along you are, and see key milestones week-by-week.

Your estimated due date (often called EDD) is a planning target, not an exact prediction. Babies commonly arrive anywhere between 37 and 42 weeks. Use this tool as a starting point, then confirm the date with your health care provider at your first prenatal visit.

Pregnancy Calculator: Calculate Your Estimated Due Date

The calculator supports four input methods. Pick the one that matches the information you have right now.

• Last menstrual period (LMP): Enter the first day of your last period and your average cycle length.
• Conception date: Enter the date you believe fertilization occurred.
• IVF transfer date: Enter your transfer date and whether it was a day-three or day-five embryo.
• Ultrasound scan: Enter the estimated due date from your ultrasound report.

Each method uses a slightly different formula, but all produce an estimated due date along with a week-by-week timeline. Results are estimates. They do not replace guidance from a qualified provider.

How to Calculate Your Due Date From Your Last Period

The most common way to calculate your due date is from the timing of your last period. Providers have used this approach for decades because most people remember their last period date more reliably than other fertility signals.

First Day of Your Last Menstrual Period

This method counts 40 weeks (280 days) from the first day of your last menstrual period. It assumes a 28-day cycle with ovulation around day 14.

If your cycle length differs from 28 days, the calculator adjusts. A longer cycle pushes the estimated due date later. A shorter cycle pulls it earlier.

What if you don't know the date of your last period? Skip to the conception date or ultrasound options below. If your periods are irregular, an early ultrasound scan often gives a more reliable estimate.

Conception Date

If you tracked ovulation (using ovulation test strips, basal body temperature charting, or both), you may know your approximate date of conception. Pregnancy from the conception date lasts approximately 38 weeks (266 days).

This method can be more accurate than LMP when your cycle is irregular or longer than average. Still, pinpointing the exact moment of fertilization is difficult. Sperm can survive several days, so conception may have happened a day or two after intercourse.

IVF Transfer Date

For in vitro fertilization (IVF), the calculation is more precise because the transfer date is known exactly.

• Day-five embryo: Add 261 days (approximately 38 weeks minus 5 days) from the transfer date, or equivalently 263 days from fertilization age.
• Day-three embryo: Add 263 days from the transfer date.

Your fertility clinic will confirm these numbers, but the calculator gives you a quick reference while you wait for your first prenatal appointment.

Ultrasound Scan

An early ultrasound (typically between 8 and 12 weeks) measures the fetus to estimate gestational age. If your provider has already given you an estimated due date from an ultrasound scan, enter it directly and the calculator will build out your week-by-week timeline from there.

Ultrasound dating is considered the most accurate method in early pregnancy, especially when the LMP is uncertain or periods are irregular.

How Far Along Are You in Your Pregnancy

"How far along am I?" is one of the first questions after a positive pregnancy test. The answer is counted in gestational weeks, starting from the first day of your last menstrual period.

Here is a quick reference:

• First trimester: Weeks 1 through 13
• Second trimester: Weeks 14 through 27
• Third trimester: Weeks 28 through 40

So if today is 10 weeks past your LMP, you are 10 weeks pregnant and in your first trimester. The calculator shows this automatically along with the number of days remaining until your estimated due date.

Keep in mind that "weeks pregnant" includes about two weeks before conception actually occurred. That is just how the standard counting system works.

Week-by-Week Pregnancy and Early Pregnancy Milestones

Tracking milestones week-by-week helps you know what to expect at each stage of pregnancy.

First trimester key milestones (weeks 1 to 13)

• Week 4 to 5: A pregnancy test can usually detect the hormone hCG. This is often the earliest you can confirm pregnancy.
• Week 6: A fetal heartbeat may be visible on ultrasound.
• Week 8 to 9: Major organs begin forming. Your first prenatal visit often happens around this time.
• Week 12 to 13: The risk of miscarriage drops significantly. Many people share the news after this point.

Second trimester highlights (weeks 14 to 27)

• Week 16 to 20: You may start to feel fetal movement, sometimes called "quickening."
• Week 18 to 22: The anatomy scan ultrasound checks the baby's development in detail.

Third trimester highlights (weeks 28 to 40)

• Week 28: The fetus reaches a significant viability milestone.
• Week 36: Your provider may begin weekly prenatal visits.
• Week 37: Pregnancy is considered "early term." Delivery any time from here forward is within the normal range.
• Week 40: Your estimated due date. Only about 5% of babies arrive on this exact day.

Can Your Due Date Change After an Ultrasound

Yes, your due date can change. If an early ultrasound shows the fetus is measuring differently than expected, your health care provider may adjust the estimated due date.

This happens most often when the LMP date is uncertain, cycles are irregular, or the ultrasound measurement differs from the LMP calculation by more than about a week. An adjusted due date based on ultrasound is typically more accurate than one based on period dates alone.

Your due date may also be adjusted later in pregnancy, though this is less common. Later ultrasounds are less reliable for dating because fetal growth rates vary more in the second and third trimesters.

A changed due date does not mean anything is wrong. It simply means your provider has better information to estimate when your baby will arrive.

Due Date Calculator for Conception and Last Period Compared

The two most popular methods for calculating your due date are LMP and conception date. Here is how they differ.

Both methods should produce a similar estimated due date if the inputs are accurate. When they disagree by more than a few days, an ultrasound scan can help your provider decide which date to use.

For IVF pregnancies, the transfer date method is the most precise because it removes the guesswork about when fertilization happened.

Pregnancy Due Date Calculator and Your Estimated Due Date

Your estimated due date is a planning guide. It helps you and your provider schedule prenatal care, prepare for delivery, and track fetal development along the way.

A few things to remember:

• Most pregnancies last between 37 and 42 weeks. Arriving "on time" covers a wide window.
• Only about 1 in 20 babies is born on the exact due date.
• The calculator provides an estimate. It is not a medical diagnosis or a guarantee.
• Confirm your due date with your health care provider, especially if you have irregular periods or other factors that could affect dating.

Bookmark this page to check your week-by-week progress anytime. For medical questions about your pregnancy, always reach out to your provider.