Pregnancy is typically calculated from the first day of your last menstrual period (LMP). This means that even though conception usually occurs around two weeks after your LMP, you are considered to be two weeks pregnant at the time of conception. To calculate your pregnancy weeks, count from the first day of your LMP. For example, if your LMP was on January 1st, you would be considered four weeks pregnant on January 29th. It is important to note that this method may not be accurate for everyone, especially those with irregular periods or who have conceived through fertility treatments. If you are unsure about how many weeks pregnant you are, it is best to consult with a healthcare professional who can provide more accurate information based on your individual circumstances.