To calculate the duration of your pregnancy, you need to count the number of months that have passed since your last period on April 17th. As of today's date, you can count the number of full months that have elapsed. For example, if it is currently September, then five full months would have passed. However, keep in mind that this calculation may not be accurate for determining the exact gestational age of your baby. It is best to consult with a healthcare professional who can provide more precise information based on medical tests and examinations.