Pregnancy calculators provide estimates within 1-2 weeks of actual delivery. Only 4% of babies are born exactly on their due date. About 60% arrive within one week, and 90% within two weeks of the estimated date. Accuracy depends on cycle regularity, ovulation timing, and the calculation method used. IVF transfer dates offer the highest accuracy (±3 days), followed by ultrasound dating and conception dates.

The most common method is to add 280 days (40 weeks) to the first day of your last menstrual period (LMP). Alternatively, add 266 days to your conception date, or use your IVF transfer date minus 14-19 days to calculate your equivalent LMP. Healthcare providers often verify and adjust this date using early ultrasound measurements, especially scans performed before 13 weeks.

Yes, your healthcare provider may adjust your due date based on early ultrasound measurements, particularly from scans performed between 8-13 weeks. These early ultrasounds can more accurately date pregnancy than LMP calculations, especially for women with irregular cycles or uncertain ovulation timing. However, due dates typically aren't changed after 20 weeks unless there's significant discrepancy.

Count the number of weeks from the first day of your last menstrual period to today. For example, if your LMP was 10 weeks ago, you are 10 weeks pregnant. Pregnancy is measured in weeks and days (e.g., 10 weeks 3 days). Use our pregnancy calculator above to get your exact gestational age instantly.

If you don't know your LMP date, your healthcare provider can use an early ultrasound (dating scan) to estimate your due date. Ultrasounds performed in the first trimester (before 13 weeks) measure the fetus and provide accurate pregnancy dating. You can also use conception date or IVF transfer date if you know those dates.

LMP stands for Last Menstrual Period. It refers to the first day of your last menstrual period before you became pregnant. This date is used as the starting point for calculating your due date and gestational age. Even though conception typically occurs about 2 weeks after your LMP, pregnancy is counted from the LMP date because it's easier to identify than the exact conception date.

For most accurate results, take a pregnancy test on the first day of your missed period or later. Some sensitive early detection tests can detect pregnancy 5-6 days before your missed period (about 10-11 days after ovulation), but results may be less reliable. The pregnancy hormone hCG needs time to build up in your system after implantation.

Pregnancy is divided into three trimesters: First trimester is weeks 1-13, second trimester is weeks 14-27, and third trimester is weeks 28-40+. Use our pregnancy calculator to determine your current week and trimester. Each trimester brings different developmental milestones, symptoms, and prenatal care needs.

IVF due dates are calculated from the embryo transfer date. For a Day 3 transfer, subtract 17 days from the transfer date to get your equivalent LMP, then add 280 days. For a Day 5 transfer, subtract 19 days. This method is more accurate than standard LMP calculations because the exact fertilization and transfer dates are known.

Pregnancy is dated from the first day of your last period because it's easier to identify than the exact conception date. Most women know when their period started, but conception date (ovulation + fertilization) is harder to pinpoint. This standard method has been used for decades and provides consistency in medical care, even though actual conception typically occurs about 2 weeks after the LMP.