It can be confusing to calculate your pregnancy timeline accurately. The best way to determine your gestational age is through ultrasound measurements taken by your healthcare provider. While it's common for there to be slight variations in estimated due dates, ultrasounds are considered more accurate than calculations based on menstrual cycles alone. If you have concerns about the difference in dates, it's always best to consult with your healthcare provider for clarification and guidance. They will be able to provide you with accurate information based on your specific circumstances.