Here we will see how to check the credit balance of the iTunes Card charged on your iOS device (iPhone or iPad) or computer (Mac or Windows).
iPhone/iPad - Use/charge iTunes Card (code) Mac/Windows - Use/charge iTunes Card (code)
iPhone/iPad
Here we use the screen of the iPhone to check the credit balance, but you can also check it on the iPad in the same way.
Mac/Windows
Here we use the Mac screen to check the credit balance, but you can check it in the same way on Windows. For other iTunes/App Store usage and settings, please see here.