Due Date Calculator
Calculate your due date from your last menstrual period or conception date.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Request a ToolHow to Use the Due Date Calculator
This calculator estimates your pregnancy due date using two methods. Here is how to use it:
- Choose your date type. Select "Last Menstrual Period (LMP)" if you know the first day of your last period, which is the standard clinical method. Select "Conception Date" if you tracked ovulation or had a monitored cycle and know the approximate date of conception.
- Enter your date. Use the date picker to enter the relevant date. You can type the date directly or use the calendar popup.
- Read your results. The calculator shows your estimated due date, current gestational age in weeks and days, trimester, and days remaining until your due date.
Results update instantly. Use Share to send your result to a partner or provider, or Copy to paste it elsewhere.
About the Due Date Calculator
This calculator uses Naegele's rule, the standard obstetric method for calculating due dates. The formula adds 280 days (40 weeks) to the first day of your last menstrual period. When using a conception date, the calculator adds 266 days (38 weeks), since conception typically occurs around day 14 of a standard 28-day cycle.
Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after. Your healthcare provider may adjust your due date based on ultrasound measurements, especially if your cycles are irregular or longer than 28 days. This calculator is for informational purposes and does not replace medical advice.
Frequently Asked Questions
How accurate is a due date calculated from LMP?
LMP-based due dates are accurate to within about two weeks for most women with regular 28-day cycles. An early ultrasound (before 13 weeks) is considered more accurate and is typically used to confirm or adjust the due date. If your cycles are irregular or longer than 28 days, the LMP method may overestimate how far along you are.
What is Naegele's rule?
Naegele's rule is a standard way to calculate the estimated due date: take the first day of the last menstrual period, add one year, subtract three months, and add seven days. The result is the same as adding 280 days (40 weeks) to the LMP date. This has been the standard clinical method since the 19th century and remains widely used today.
How many weeks is a full-term pregnancy?
A full-term pregnancy is 39-40 weeks from the last menstrual period. "Early term" is 37-38 weeks, "full term" is 39-40 weeks, "late term" is 41 weeks, and "post-term" is 42 weeks or more. Babies born before 37 weeks are considered preterm. The American College of Obstetricians and Gynecologists defines full term as 39 weeks 0 days through 40 weeks 6 days.
When does each trimester start and end?
The first trimester runs from weeks 1 through 12. The second trimester covers weeks 13 through 26. The third trimester begins at week 27 and continues through birth at around week 40. Each trimester brings distinct developmental milestones and physical changes. Most prenatal screening tests are scheduled at specific points within these trimesters.