The method to work out your due date from your LMP is to add 280 days to the first day of your last menstrual period. This will give you a rough guide of when your baby is due to be born.
The LMP (Last Menstrual Period) method calculates your due date by adding 280 days (40 weeks) to the first day of your last menstrual period. This is the standard method used by most healthcare providers and is based on Naegele's Rule.
Naegele's Rule is the standard formula for estimating a pregnancy due date. It works by taking the first day of the last menstrual period, adding one year, subtracting three months, and adding seven days. The result is the same as adding 280 days to the LMP date.
The LMP method is accurate for women with regular 28-day cycles. Only about 5% of babies are born exactly on their due date, and most births occur within two weeks before or after the estimated date. Ultrasound measurements can refine the estimate, especially in early pregnancy.
Pregnancy is dated from the last menstrual period because it is a known, observable date, whereas the exact date of conception is often uncertain. Ovulation and conception typically occur about two weeks after the LMP, which is why the standard 40-week pregnancy actually includes about two weeks before conception occurred.
If your menstrual cycles are irregular, the LMP method may be less accurate for you. In such cases, an early ultrasound (typically between 8 and 14 weeks) is the most reliable way to estimate gestational age and due date. Consult your healthcare provider for personalized guidance.