Amount to show on a bill form

Question

My company is currently setting up an online billing portal for our customers. I was curious as this question went back and forth a bit between developers and testers: When showing the input form for the amount a customer wishes to pay, do you set the default to be the max amount owed by the customer? Taking a look around at sites when I pay my own bills I tend to see three different setups:

1. Max amount owed is in the input
2. Nothing is put in
3. Button options to pay off max, minimum, or your own input

In general we agree that your max and min amount should be shown on the screen somewhere (it's annoying to go look for your bill when the site can show amount owed). Is there a standard or what seems most friendly? Option 1 is nice cause it's all there but might annoy a customer a bit or a customer might accidentally pay off a large amount without realizing it (sounds dumb but you know it'll happen to someone). Option 2 gives the feeling of payment control to a customer but annoys them with having to input an amount everytime. Option 3 looks to be a middle ground but seems like a bit more unneeded work and upkeep when 1 and 2 are simpler and cleaner to look at.

Answer 1

Can you query your own payment system to see what kind of payments your customers are making most often? Then set that as your default. I'd give them all options, though, including max, min, and custom.

Answer 2

I'd instinctively go for (1) - default to full amount. However, I grew up in an environment where debt wasn't taken lightly.

You should have a confirmation page with the amount payable anyway - since I might enter a wrong amount and press enter. So the "paying to much" argument doesn't really cut it.

Using the full amount as default can be a slight nudge towards paying all of it. With a major volume of payments, this might be notable.

I would not default to smaller amount. A customer might overlook that it's not the full amount, consider the deal done and miss the further payments. With a good layout ("Amount Remaining") that can be avoided in almost all cases - but with a large trade volume, you might create a few annoyed customers.