Pregnancy Due Date Calculator
Estimate your due date, current week, and trimester based on your last menstrual period.
How is a due date calculated?
The most common method, known as Naegele's rule, estimates a due date as 280 days (40 weeks) after the first day of your last menstrual period (LMP). This calculator adjusts that estimate slightly if your average cycle length is longer or shorter than the typical 28 days, since ovulation timing shifts along with cycle length.
Understanding pregnancy weeks and trimesters
Pregnancy is measured in weeks starting from the first day of your LMP, even though conception typically occurs about two weeks later. Pregnancy is divided into three trimesters: the first trimester spans weeks 1 through 13, the second spans weeks 14 through 27, and the third spans weeks 28 through 40.
Keep in mind
Only about 5% of babies are born on their exact estimated due date — most arrive within a couple of weeks before or after. Irregular cycles, uncertain LMP dates, or later ultrasound measurements can all shift this estimate. This is an estimate for informational purposes only and not medical advice.
Frequently Asked Questions
Can this calculator tell me if I'm pregnant?
No — this calculator estimates a due date, current week, and trimester once pregnancy is already confirmed; it does not diagnose pregnancy itself. If you think you might be pregnant, a home pregnancy test (taken after a missed period for the most reliable result) or a blood test from a healthcare provider is the way to confirm it.
What are early pregnancy symptoms in week 1?
Technically, pregnancy dating starts from your last menstrual period, before conception has even occurred, so there typically aren't pregnancy symptoms yet in week 1. Early symptoms like fatigue, breast tenderness, nausea, or a missed period usually don't appear until several weeks later, around the time of a missed period.
What are signs of pregnancy before a missed period?
Some people notice mild cramping, light spotting (implantation bleeding), breast tenderness, fatigue, or a heightened sense of smell in the days before a missed period, though many people notice no symptoms at all this early. These signs are not conclusive, and a pregnancy test remains the most reliable way to confirm pregnancy.
How accurate are due date calculators?
Due date calculators based on your last menstrual period provide a solid estimate, but only about 5% of babies are actually born on that exact date — most arrive within about two weeks before or after. An early ultrasound (typically in the first trimester) is generally considered the most accurate method for confirming a due date.
What's the difference between due date by LMP and by conception date?
Calculating from your last menstrual period (LMP) adds 280 days (40 weeks) and is the standard clinical method, since conception date isn't usually known precisely. Calculating from a known conception date instead adds about 266 days (38 weeks). Both methods estimate roughly the same due date when cycles are regular and typical in length.
What trimester am I in, and how many weeks pregnant am I?
Pregnancy weeks are counted from the first day of your last menstrual period. The first trimester covers weeks 1-13, the second trimester covers weeks 14-27, and the third trimester covers weeks 28-40. Enter your LMP date above and the calculator will show your current week and trimester automatically.
Is a due date calculator as accurate as an ultrasound?
An early ultrasound is generally considered more precise than an LMP-based calculation, especially for people with irregular cycles or uncertain LMP dates, since it measures the fetus directly. This calculator gives a useful early estimate, but your healthcare provider may adjust your due date after an ultrasound.
What if my menstrual cycle is irregular — does that affect the calculation?
Yes, irregular or unusually long/short cycles can shift when ovulation actually occurs, which makes LMP-based due date estimates less precise. This calculator lets you adjust for average cycle length to improve the estimate, but an ultrasound is typically more reliable if your cycles are very irregular.