How can I suggest another way to calculate a estimated credit card payment amount?

And how, may I ask, should Quicken determine what the future balance of your credit card on a future cutoff date, perhaps even several months into the future is going to be? That would require one big crystal ball, I'd say.

When setting up Scheduled Reminders, if the "Current Credit Card Balance" option doesn't work for you to estimate the payment amount, try setting it to "Previous payments", "last 3 (or 6) payments" to get an estimated average amount.