About Pregnancy Due Date Calculator
The Pregnancy Due Date Calculator estimates your expected delivery date using Naegele's rule, which adds 280 days or 40 weeks from the first day of your last menstrual period. This method has been the standard in obstetrics for over two centuries and remains the most common approach for estimating due dates. Alternatively, you can calculate based on your conception date if known, which the tool converts by subtracting approximately two weeks to align with the LMP-based timeline. The calculator also determines your current pregnancy week and trimester by comparing today's date against your calculated timeline, helping you track your progress through the three trimesters of pregnancy. Only about five percent of babies arrive exactly on their estimated due date, and a full-term pregnancy is considered anywhere from 37 to 42 weeks, so the date should be viewed as a general guide rather than a precise prediction. Healthcare providers may adjust due dates based on early ultrasound measurements, particularly in the first trimester. This tool is helpful for planning and tracking fetal development stages throughout your pregnancy.
When to Use This Calculator
Use this calculator as soon as you find out you're pregnant to get an immediate estimate of your due date. It helps with planning maternity leave, scheduling prenatal appointments, and knowing which trimester milestones are coming up. Many parents use it to plan for the baby's arrival, such as when to set up the nursery or attend birthing classes, which are often recommended in the third trimester. Healthcare providers will also use your due date to schedule important screenings, like the glucose tolerance test usually done between weeks 24 and 28, and the anatomy scan around week 20. Keep in mind that if you have irregular periods or can't remember your LMP, an early ultrasound between 8 and 13 weeks is the most accurate way to date your pregnancy.
How to Use This Calculator
Start by selecting your preferred calculation method. Most women use the LMP option, where you enter the first day of your last menstrual period. The calendar defaults to today's date, so you'll need to adjust it backward to the actual LMP date. For example, if your last period started on March 15, 2026, select that date from the date picker. The calculator will add 280 days and give you a due date of December 19, 2026. It also shows you're currently in week 16 if today is July 8, 2028, which would put you in the second trimester. If you know your exact conception date instead, switch to the second option and enter that date. The calculator works backwards by subtracting 14 days to align with the standard 40-week timeline. This gives you the same due date as the LMP method would.
How to Interpret Your Results
Your estimated due date is shown prominently at the top of the results. For example, if your LMP was March 15, 2026, your due date would be December 19, 2026. The countdown shows how many days remain until that date. The calculator also tells you your current pregnancy week. If you're at week 16, you're in the second trimester, which spans weeks 13 through 26. The estimated conception date is also shown, calculated as 14 days after your LMP. The informational note reminds you that only 5 percent of babies arrive on their exact due date, so don't treat it as a deadline. Full term runs from 37 to 42 weeks, meaning your baby could arrive anytime from late November through late December in this example, and that's all completely normal.