Be able to have a fixed day of payment

If I buy a running subscription for a Realm on the 20th then the next payment will be on the 19th and the one after that the 18th. This will eventually create a gap for me if I don't have the money when the withdrawal is made. I want to make the payment same day each month. 

Yes, I could buy realm manually each month but even if I choose the 3-months at a time, it's still more expensive, not to mention a hassle.