You will find your Expiration date under Account settings when you click your Username/ email at the top when logged in.
Click View Available Plans to see your options. If you had an expiration date it would appear here. Or you can cancel recurring from this section, if you are not on a one off plan. If you don't see your Pro / or Lite subscription here, you may need to log out and try other emails you might have used to register to see if you Pro or Lite plan is in another account instead. Thanks for Piktochart-ing!