Calculators

Health

Use the pregnancy calculator to find your estimated due date and see pregnancy progress in weeks and trimesters. Choose your pregnancy calculation method and input either:

• Last menstrual period, LMP
• Conception date
• Gestational age by ultrasound
• IVF transfer date

The pregnancy calculator finds the estimated due date, estimated conception date, and how far along the pregnancy is in terms of weeks. It also shows the pregnancy trimester schedule, and the pregnancy timeline week-by-week.

How Far Along Am I, and When is My Due Date?

There are many methods to calculate how many weeks pregnant you are. Obstetricians typically use the first day of your last menstrual period, LMP, as the basis for calculating your due date. Then they use Naegele's Rule to calculate the estimated date of delivery or EDD by hand.

Developed in the 1800s based on the observation that the average human pregnancy lasts 280 days, the formula for Naegele's Rule is:

• Note the LMP date
• Count back 3 months
• Add 7 days to that date
• Add one year to get estimated due date

It might seem strange to use a person's period date to calculate pregnancy, because you aren't pregnant when you are menstruating. But the first day of a period marks the start of the hormone cycle that prepares the body for fertility and egg implantation.

You can also use a calendar to estimate a due date. Since pregnancies generally last 40 weeks, you can count forward 40 weeks from the start of the LMP to find the due date. Although straightforward, this method is a bit more time consuming than calculating due date using Naegele's Rule.

Example Due Date Calculation

Say a person's LMP was June 4, 2025. Use Naegele's Rule to estimate their due date.

• LMP = June 4, 2025
• June 4 minus 3 months = March 4
• March 4 plus 7 days = March 11
• Add one year to get estimated due date of March 11, 2026

Keep in mind that any pregnancy calculation will result in an estimated due date. It's hard to predict a due date with absolute certainty because pregnancy length varies naturally, and many biological factors influence the timing of a baby's birth. The American College of Obstetricians and Gynecologists (ACOG) advises that a typical pregnancy can last 40 weeks, plus or minus 2 weeks.

Calculate Pregnancy Due Date

The calculator finds pregnancy progress and due date using:

• The first day of the last menstrual period
• First trimester ultrasound results
• Conception date
• IVF transfer date
• Back-calculating from your due date

Select your preferred method in the pregnancy calculator to find your due date. Read on to learn how we do these due date calculations.

How Far Along Am I Based on Last Menstrual Period?

Pregnancy in humans lasts 40 weeks starting with the first day of the last menstrual period. Development of the baby during this 40-week time frame is called gestation, and it is marked in weeks as gestational age.

To find expected due date by hand you can use Naegele's Rule explained above. Or you can add 40 weeks to the date of the last menstrual period by counting weeks on a calendar.

To find how far along you are in a pregnancy, count the number of weeks from your LMP to today, or any date you choose. You can count the days on a calendar or use our Date Difference Calculator to find the number of days between your LMP and today, or any date.

To calculate how far along you are using LMP:

• Count the days from your LMP start date to today
• Divide by 7 to get weeks and remaining days

Example: The first day of your last period was October 1. Today is December 1.

• October 1 to December 1 = 61 days
• 61 days ÷ 7 = 8 weeks, 5 days pregnant

Calculate How Far Along You Are if You Have Longer or Shorter Menstrual Cycles:

• Adjust your starting date: LMP + (Cycle Length − 28 Days)
• If your number is negative, count back from your LMP and note your adjusted LMP start date
• If your number is positive, count forward from your LMP and note your adjusted LMP start date
• Count the days from your adjusted LMP date to today
• Divide by 7 to get weeks and remaining days

Longer Cycle Example: The first day of your last period was October 1. Today is December 1. Your average cycle length is 32 days.

• Adjust the start date: October 1 + (32 − 28 Days)
  October 1 + 4 = October 5
• October 5 to December 1 = 57 days
• 57 days ÷ 7 = 8 weeks, 1 day pregnant

Shorter Cycle Example: The first day of your last period was September 29. Today is January 1. Your average cycle length is 25 days.

• Adjust the start date: September 29 + (25 − 28 Days)
  September 29 − 3 = September 26
• September 26 to January 1 = 98 days
• 98 days ÷ 7 = 14 weeks pregnant

How Far Along Am I Based on Ultrasound Results?

Ultrasound gestational age estimates are the most accurate way to determine how many weeks pregnant you are, mainly in the first trimester.

The ultrasound technician measures your baby's size and compares it to standard embryo growth charts for early pregnancy. This establishes the baby's gestational age, which becomes the basis for tracking the pregnancy timeline moving forward. If the ultrasound results in a very different date than your last period calculation, your provider may change your due date to fit the ultrasound findings.

You can input gestational age into the calculator to find your estimated due date. By hand you can use any calendar, starting with gestational age on ultrasound day. Then count forward until you reach 40 weeks to find your due date.

How Many Weeks Pregnant Am I Using IVF Transfer Date?

A successful in vitro fertilization, IVF, is essentially the same as conception date, making pregnancy dating very precise. To calculate gestational age, add 14 days to your IVF transfer date. Then count backwards that number of days to find an LMP equivalent date. This date is your pregnancy starting point.

Calculate How Far Along You Are in Pregnancy for a Day 3 IVF Transfer:

• 3 + 14 = 17. So count back 17 days from your transfer date to get your LMP equivalent

Calculate How Far Along You Are in Pregnancy for a 5 Day IVF Transfer:

• 5 + 14 = 19. So count back 19 days from your transfer date to find your LMP equivalent

Once you have the LMP equivalent date, you can use the LMP method to calculate your pregnancy weeks using a calendar.

How Far Along Am I Based on Conception Date?

Fetal age or conceptional age measures pregnancy from your conception date rather than your LMP. Since conception typically occurs about 14 days after the beginning of your last period, fetal age is 2 weeks shorter than gestational age. To convert fetal age to gestational age (what doctors use), add 2 weeks to your conception date.

Tracking ovulation or knowing the specific conception date makes this method more accurate.

Calculate How Far Along in Pregnancy You Are Using Conception Date:

• Count days from conception to today
• Divide by 7 to convert to weeks and days (fetal age)
• Add 2 weeks to find gestational age, which is like calculating pregnancy from LMP

Example: If conception occurred on October 15 and today is December 1:

• Fetal age in days, October 15 → December 1 = 47 days
• Convert to weeks and days: 47 ÷ 7 = 6 weeks, 5 days
• Add 2 weeks to get gestational age: 6 weeks, 5 days + 2 weeks = 8 weeks, 5 days pregnant

How Far Along Am I Based on My Due Date?

Count backward from your estimated due date to calculate how many weeks pregnant you are. A full-term pregnancy is 280 days which is equal to 40 weeks.

Calculate how far along you are in pregnancy using your due date:

• Count days from today to your due date, or use our Date Difference Calculator to find how many days left in your pregnancy
• Subtract that number from 280 days to find how many days pregnant you are
• Divide by 7 to convert to weeks

Example: If your due date is June 20 and today is December 1:

• Count forward, December 1 → June 20 = 201 days
• Days pregnant: 280 − 201 = 79 days pregnant
• Convert to weeks: 79 ÷ 7 = 11 weeks, 2 days pregnant

Will I Give Birth on My Due Date?

Your estimated date of delivery, or EDD, is calculated as 40 weeks forward from the first day of your last menstrual period. Only about 5% of babies are born on their exact due date.

What to know:

• Your due date is an estimate
• Full term is 37–42 weeks
• First-time moms often deliver after their due date
• Your healthcare provider may adjust your due date based on ultrasound measurements

How Many Trimesters in Pregnancy?

Pregnancy is divided into three trimesters, each lasting about 13–14 weeks. Each trimester marks different stages of a baby's development, and physical and clinical changes in the pregnant person's body.

First Trimester: Weeks 1–13

• Conception and implantation occur
• Baby's organs begin forming

Second Trimester: Weeks 14–27

• The pregnant person's energy typically improves, and any nausea may decrease
• The baby's body develops, the parent's belly bump shows, and baby's movements are felt

Third Trimester: Weeks 28–40 (or until delivery)

• Baby gains most of their weight
• Baby's organs mature and the brain continues to develop

Frequently Asked Questions