It is not uncommon for there to be a slight discrepancy between the estimated gestational age provided by your doctor and the one calculated by an online pregnancy calculator. The most accurate way to determine your due date is through an ultrasound examination performed in the first trimester. This will provide a more precise measurement of fetal development and help establish a more accurate timeline for your pregnancy. Keep in mind that every woman's menstrual cycle and ovulation patterns can vary, which can affect the calculation of gestational age. Additionally, some online calculators may use different algorithms or assumptions when estimating due dates compared to medical professionals. If you are concerned about the difference in weeks between your doctor's estimate and the online calculator, it is best to discuss this with your healthcare provider who can provide further clarification based on your individual circumstances.