Authorize.Net provides a number of ways to process transactions through the payment gateway, ranging from simple "Buy Now" and "Donate" buttons to fully integrated, highly customizable Application Programming Interfaces (APIs).
CIM(Customer Information Manager) is one of them. This API is suitable when the date and/or amount is different each month.
You can learn more about CIM using following link:
You can get sample code from here:
But before this you need a test account so go through it: