To calculate the age of your pregnancy, you can use the first day of your last menstrual period (LMP) as a starting point. Counting from the first day of your LMP, you can estimate that you are around X weeks pregnant. However, keep in mind that this is just an estimation and may not be entirely accurate. It's best to consult with a healthcare professional who can perform an ultrasound or other tests to determine the exact age of your pregnancy based on fetal development. They will take into account factors such as irregular cycles and ovulation timing to provide a more accurate assessment.