Why must a user enter cents at an ATM when it only dispenses whole dollars?

Question

I live in the United States, and many of our ATMs only dispense money in $20 increments. This makes sense given the added infrastructure that would be required in the machines to dispense many different kinds of bills or coins, and that $20 is a good amount of money but not that much.

At almost every ATM I've seen, when given a free text field to enter a value for withdrawal, the user must enter the full value, including cents. For example, to withdraw $20, the user must type [2] [0] [0] [0] (with the decimal point implied before the last two digits entered). Why is this? Aren't those two last zeros entirely unnecessary?

The only other reason I can think of is that since most ATMs have transaction limits of $200-500 or so, users can't remove $2,000 in a transaction, and so by including the extra decimal places you're making the user think a bit more while entering the number, and the machine won't do anything if the user enters an incorrect value. But I'm not convinced that's the reason why.

Answer 1

I believe there are two aspects to it.

• As voronoipotato pointed out the decimal point acts as a differentiating factor to ensure you know exactly how much money you are withdrawing and dont accidentally overdraw as the decimal points acts a indicator of where the dollar ends and the cents start. While this might seem unlikely, people are prone to over paying too much as example shows where a customer overpaid comcast by thousands of dollars as he missed a decimal point . To quote the article

While paying online, Joseph Azzem accidentally sent the company $6,453 instead of the $64.53 he owed after he left out a decimal point

• The second reason is that ATM's can be used to deposit cheques as well and cheques can have cents as well and the same software backend might be used for deposits and withdrawals and hence ATM's might show the decimals for both cases

Answer 2

Legacy. Back when they only had old green-screen ATMs, they were very limited in capacity. They could only show a few dozen unique screens. They would reuse a screen prompting for amount because they didn't have the capacity to create a separate prompt for "withdraw random cash amount" from "enter amount".

By keeping the same set of screens and prompts, they could run the same program on both the green screens as well as the newer graphical displays.

ATMs are very expensive to update. One machine costs several thousand dollars, so they don't replace them until they absolutely have to. Also, they're built to be extremely durable, as they face the public in all kinds of unattended places, and the public occasionally wants to try to break in to steal the cash. The software providers know that ATMs are a 20 year investment, so their updates need to be billed as "backward compatible" or nobody will upgrade to newer software. So most of the features you see on these "newer" ATMs are really just graphic candy on top of ancient screen definitions.

Some banks use newer software that behaves more rationally, and are more user friendly, but they're in the minority.