Due Date Calculator: Get an Estimated Due Date
Important: This is an estimate based on a standard 280-day calculation from your last period, and actual delivery dates vary widely. Only about 5% of babies are born on their exact estimated due date. Always confirm timing with your healthcare provider, who may adjust this based on ultrasound measurements.
How Due Dates Are Actually Calculated
The standard method, called Naegele’s Rule, adds 280 days, 40 weeks, to the first day of your last menstrual period. This assumes a fairly standard cycle length, which is why healthcare providers often adjust the estimate using early ultrasound measurements, which can be more precise for irregular cycles.
Why Due Dates Are Estimates, Not Predictions
Full-term pregnancy is generally considered to span weeks 37 through 42, a five-week window. A due date is the statistical midpoint of a normal range, not a precise prediction, which is why the majority of births happen within a week or two of the estimated date rather than exactly on it.
Frequently Asked Questions
Why did my doctor give me a different date than a calculator?
Early ultrasound dating, particularly in the first trimester, is often considered more accurate than last-period calculations alone and may adjust your estimated date by several days.
Is it a problem if I go past my due date?
Going a few days to a week past your due date is common and not usually a concern on its own; your provider will monitor accordingly.
Related Guides
Pregnancy Guide | Pregnancy Week-by-Week | Labor and Delivery
How the Pregnancy Due Date Calculator Works
Quick answer: A pregnancy due date is an estimate, not a guaranteed delivery day. A common calculation counts 40 weeks, or 280 days, from the first day of the last menstrual period. A clinician may confirm or adjust the estimate using ultrasound and other clinical information.
Information You Can Use
| Information available | How it is commonly used |
|---|---|
| First day of the last menstrual period | Used to estimate 40 weeks from that date when cycles are reasonably regular |
| Known conception or ovulation date | May provide another estimate when timing is known with confidence |
| IVF transfer information | Dating depends on the embryo age and transfer date and should follow the fertility clinic’s estimate |
| Ultrasound measurements | Early ultrasound can establish or confirm gestational age and may change the estimated date |
Why Your Estimated Due Date May Change
Cycle length, uncertain period dates, later ovulation, irregular cycles, and ultrasound findings can affect pregnancy dating. According to the American College of Obstetricians and Gynecologists, first trimester ultrasound is the most accurate ultrasound method to establish or confirm gestational age. Your maternity care professional should document the best obstetric estimate.
What the Result Means
The result gives a useful planning date and an estimated gestational age. Many healthy births occur before or after the exact date. Use the estimate to guide conversations and appointments, but follow the dating recorded by your obstetrician, midwife, or other qualified maternity care professional.
Frequently Asked Questions
Is a due date exactly 40 weeks from conception?
Pregnancy weeks are usually counted from the first day of the last menstrual period, about two weeks before conception in a typical cycle. That is why standard pregnancy dating is approximately 40 weeks from the last period rather than 40 weeks from conception.
What if my menstrual cycle is irregular?
A last period estimate may be less reliable. Contact your maternity care professional, who may use early ultrasound and clinical history to establish the best estimate.
Can an ultrasound change my due date?
Yes. A clinician may revise the estimated due date when ultrasound dating differs enough from menstrual dating under accepted clinical criteria. Do not change the date yourself based on a calculator.
Does the calculator replace medical care?
No. This calculator provides general educational information only. It cannot confirm pregnancy, assess fetal health, or replace prenatal care.
Continue Your Pregnancy Journey
Follow changes with our pregnancy week by week guide, prepare using the main pregnancy guide, and learn what to expect during labor and delivery.
Trusted Medical Source
Medical disclaimer: This information is educational and is not a diagnosis or a substitute for care from your obstetrician, midwife, or other qualified health professional. Seek urgent local medical care for severe pain, heavy bleeding, fainting, breathing difficulty, or another emergency concern.
Editorially reviewed using our editorial policy and sources and references standards.