Pregnancy Due Date Calculator
Enter your last menstrual period to calculate your due date and track your pregnancy.
About this calculator
A pregnancy due date, also called the estimated date of delivery, is the day a pregnancy reaches 40 weeks. It helps you and your healthcare team plan prenatal visits, schedule screening tests at the right time, and keep track of how the baby is developing. It is an estimate rather than a deadline: most babies are born in the weeks around the due date, not on it.
Pregnancy is counted from the first day of your last menstrual period (LMP), not from the day of conception. That is because the first day of a period is usually easy to remember, while the exact day of ovulation and conception is rarely known. In a typical 28-day cycle, ovulation happens around day 14, so by the time conception occurs you are already considered about two weeks pregnant. This is why a full-term pregnancy is described as 40 weeks, even though the baby develops for about 38 weeks after conception.
How to use this calculator
Enter the first day of your last menstrual period in the date field. The calculator then shows three results. Due Date is your estimated date of delivery. Current Week is the number of full weeks that have passed since your LMP, shown as Week X of 40. Trimester tells you whether you are in the first, second or third trimester. A progress bar divided into the three trimesters marks where you are across the 40 weeks. When the page first opens, the date is set to ten weeks before today as an example, so remember to replace it with your own date. Your date is stored in the page address, so you can bookmark the page; keep in mind that anyone you share the link with will see the date you entered.
The method
This calculator uses Naegele's Rule, the standard method clinicians have used for well over a century. It adds 280 days, which is exactly 40 weeks, to the first day of your LMP. A common shortcut gives the same answer: add one year, subtract three months, and add seven days. To find your current week, the calculator counts the days from your LMP to today and divides by seven, counting only completed weeks. The week shown is capped at 42, and it shows 0 if fewer than seven days have passed or if the date entered is in the future.
Trimesters in this calculator are grouped by completed weeks
Weeks 0 to 12 are the first trimester, weeks 13 to 27 are the second, and week 28 onward is the third. Some sources draw the boundaries a week differently, for example ending the first trimester at the end of week 13, so you may see slightly different groupings elsewhere.
A worked example
Suppose the first day of your last period was January 1, 2026. Adding 280 days gives a due date of October 8, 2026. The shortcut agrees: January 1 plus one year, minus three months, plus seven days is October 8. If today were April 15, 2026, then 104 days would have passed since the LMP. That is 14 full weeks and 6 days, so the calculator would show Week 14 of 40 and place you in the second trimester. On April 1, 2026, 90 days after the LMP, it would show Week 12 and the first trimester, and on July 20, 2026, it would show Week 28 and the third trimester.
How to interpret your results
Clinicians often write gestational age as weeks plus days, so the example above would be written as 14+6, meaning 14 weeks and 6 days. The calculator shows only the completed weeks. Your due date marks 40 weeks, but a full-term birth is defined as one between 39 weeks and 40 weeks 6 days. Births from 37 weeks to 38 weeks 6 days are called early term, and from 41 weeks they are called late term. Only a small share of babies, often quoted at around 4 to 5 percent, arrive on the exact due date. It is more helpful to think of the due date as the middle of a window of several weeks.
Practical tips
If you are not sure of the first day of your last period, use your best estimate and tell your healthcare provider that the date is uncertain. Note your cycle length too, because it affects how accurate the estimate is. Use the current week to follow general information about each stage of pregnancy, and bring your questions to your prenatal appointments.
Limitations
Naegele's Rule assumes a regular 28-day cycle with ovulation around day 14. If your cycles are longer, shorter or irregular, or if you recently stopped hormonal contraception or were breastfeeding, the estimate may be off by a week or more. The calculator does not adjust for cycle length and does not support dating from a known conception or embryo transfer date, as with IVF. Your healthcare provider will confirm your due date, usually with an ultrasound. An ultrasound in the first trimester, which measures the length of the embryo or fetus, is generally considered the most accurate way to date a pregnancy, and your provider may change your due date based on it. This calculator is for general information only and is not medical advice. If you think you may be pregnant, or have any concerns during pregnancy, contact a healthcare provider.
Frequently Asked Questions
More fitness calculators
- TDEE CalculatorCalculate your Total Daily Energy Expenditure and calorie targets for cutting, maintaining, or bulking.
- BMI CalculatorFind your Body Mass Index and see which weight category you fall into.
- Body Fat CalculatorEstimate your body fat percentage using the accurate US Navy tape measurement method.
- Macro CalculatorGet your daily protein, carb, and fat targets based on your TDEE and goal.