Due Date Calculator
Calculate your due date from your last period, ovulation date or ultrasound dating, then see baby growth, a checkup timeline and leave dates in one place.
If your cycle is longer than 28 days, ovulation comes later and the due date moves later by the same amount. Choose your cycle and we adjust automatically.
Use this if you know your ovulation or conception date, for example from fertility tracking, IUI or IVF.
For example, if you were told “12 weeks 3 days”, enter 12 on the left and 3 on the right. Ultrasound dating from your clinic is the most accurate method.
40-week pregnancy track
Your baby this week
The horizontal axis shows pregnancy weeks and the vertical axis the average fetal weight. The orange dot marks where your baby is now. Real size varies a lot from baby to baby, so use this as a rough guide.
When will the baby arrive? Births by week
Few babies arrive exactly on the due date. The gray dates below show where each range falls on your calendar. (Shares are based on 2023 U.S. CDC birth statistics.)
Checkups & preparation timeline (calculated from your dates)
The timing and type of tests depend on your provider and your health. Confirm the schedule with your care team.
Leave, insurance & visit dates (calculated from your dates)
Rules and benefits differ by employer, state and insurer, and they can change. Confirm with your HR department, your insurer and your state agency.
You are already past 40 weeks. Be sure to check with your provider about when the baby is expected.
How to use
How your due date is calculated
A due date, formally the estimated date of delivery, is the day you reach 40 weeks of pregnancy. This due date calculator offers the three methods providers use. With the last period method you enter the first day of your last menstrual period and, if your cycles are not 28 days, your usual cycle length. With ovulation or conception you enter the date of ovulation or an exact conception date, for example from fertility tracking, IUI or IVF. With ultrasound you enter the date of a scan and the gestational age it reported. Each method produces the due date, weeks and days pregnant today, your trimester, a progress track, an estimate of your baby’s size and a calendar of the checkups and decisions ahead.
Naegele’s rule and cycle adjustment
The standard calculation, known as Naegele’s rule, adds 280 days to the first day of the last period. You can do it by hand by counting back three months from that day and adding seven days and a year. It assumes a 28-day cycle with ovulation around day 14. If your cycle is 35 days, ovulation probably happened around day 21, so the due date moves a week later, and the calculator makes that correction when you pick your cycle length. When you enter an ovulation or conception date, the due date is 266 days after it, because conception takes place at ovulation.
Due date = last period + 280 days + (cycle length − 28) | Due date = ovulation + 266 days
Why ultrasound dating can be more accurate
Not everyone remembers their last period or ovulates on schedule. A first-trimester ultrasound measures the embryo from head to rump, and because early growth is so uniform, the measurement can date the pregnancy to within about five to seven days. The American College of Obstetricians and Gynecologists generally recommends changing the due date to the ultrasound-based date when it differs from the last-period date by more than five days at 9 weeks or earlier, or more than seven days from 9 to 16 weeks. Your provider will decide; if they give you a due date, use theirs.
How likely is it to deliver on the due date?
Not very. Only about 4 percent of babies are born on their due date, and most are born in the weeks around it. The bars on this page show the share of U.S. births by week: roughly 10 percent are preterm (before 37 weeks), 30 percent are early term (37 to 38 weeks), 55 percent are full term (39 to 40 weeks) and about 5 percent arrive at 41 weeks or later. The gray dates under each bar translate those weeks into dates on your calendar. Think of your due date as the center of a window, and plan for the possibility that the baby comes a couple of weeks early or late.
Baby size by week
The table lists average length and weight for each week from 8 to 40, with the usual fruit-and-vegetable comparison. Through week 18 the length is measured head to rump (crown-rump length), and from week 19 it is head to heel, which is why the number jumps. These are averages, and healthy babies vary a lot.
Average baby size from week 8 to week 40
| Week | Length | Weight | Size comparison |
|---|
Values are averages commonly published in obstetric references. Always rely on your own provider’s measurements.
Prenatal care timeline in the United States
The timeline in the results turns your dates into a calendar. Typical milestones include a first prenatal visit around weeks 8 to 10, optional first-trimester screening and cell-free DNA testing between weeks 10 and 13, a detailed anatomy ultrasound between weeks 18 and 22, a glucose test for gestational diabetes between weeks 24 and 28, the Tdap vaccine between weeks 27 and 36, and a group B strep swab at weeks 36 to 37. Visits are usually monthly until week 28, every two weeks until week 36, and weekly after that. Your provider may change this based on your health.
Leave, insurance and paperwork
The United States has no national paid parental leave. The Family and Medical Leave Act (FMLA) gives eligible employees up to 12 weeks of unpaid, job-protected leave, and a growing number of states and employers offer paid leave, so check your state program and your employee handbook early. Short-term disability plans often cover about six weeks after a vaginal birth and eight weeks after a cesarean birth. Most health plans require that a newborn be added within 30 days of birth (some marketplace plans allow 60 days), so put the deadline on your calendar. The pregnancy and leave dates in the results are estimates built from your due date.
When to call your provider right away
Contact your provider or go to the hospital for vaginal bleeding, a sudden gush or steady leak of fluid, severe or constant abdominal pain, a severe headache with vision changes, a noticeable drop in the baby’s movements, or regular contractions before 37 weeks. Many providers use the 5-1-1 guideline for labor: contractions about five minutes apart, lasting about one minute, for at least one hour. Follow your own provider’s instructions, which can differ.
Frequently asked questions
How is the due date calculated from the last period?
The calculator adds 280 days, or 40 weeks, to the first day of your last period. If your usual cycle is longer or shorter than 28 days, it shifts the date by the difference, because ovulation would come later or earlier.
Can my due date change?
Yes. Providers often move the due date after an early ultrasound if the measurement disagrees with the last-period date by more than a few days. Once your provider confirms a due date, that is the one to use.
What is the most accurate way to date a pregnancy?
A first-trimester ultrasound is considered the most accurate, followed by a known conception or embryo transfer date, and then the last period. This tool supports all three.
How many weeks is a full-term pregnancy?
Full term is 39 weeks 0 days to 40 weeks 6 days. Early term is 37 weeks to 38 weeks 6 days, late term is 41 weeks, and post-term is 42 weeks or more.
What if I have irregular cycles?
The last-period method is less reliable when cycles vary. Ask your provider about an early ultrasound, and then use the ultrasound option here so your dates match.
Are the leave and insurance dates legal advice?
No. They are rough estimates to help you plan. Eligibility depends on your employer, state and plan, so confirm with HR and your insurer.
Is my data stored?
No. The calculation runs in your browser and nothing you enter is saved or sent.