I just *underpaid* my tax because of a poor interface

What if thousands of people were underpaying their tax by accident, and getting fined for it later? I can’t be the only one.

Paying your tax as a self-employed person is never fun. Some years ago I switched to a stricter accounting regime in order to ensure I was saving the correct amount of tax in advance into a separate account.

I submit my UK tax return once a year, which tells me what I should pay at the end. There’s a lot of things about accounting, tax, and the process that I am prone to forget (once a year only!), so there’s an additional burden on this interface to guide me through this complicated task successfully, without having to remember lots of little details.

Clearly I got it wrong this year: I’ve just received a letter informing me that I’d underpaid my tax, by a not insignificant amount. I won’t go into the boring details of tax, but the problem is caused at the end of the process:

1. they shock a user by incorrectly asking for a very large payment that is two tax years added together – no idea why they even show this (see ‘WHAT THE HELL??’ in my screenshot)
2. they don’t calculate and display the figure you should pay, even though the numbers needed for calculation are displayed right there. In fact, you’re mislead by a different figure. (see ‘OK, will pay right away’ in my screenshot)

Do they have any idea how error-prone this screen turns out to be?  Once again, I wonder if this is a page with an initially poor design, that’s resulted in a lot of expensive, labour-making mistakes. A few questions then…

• Are they unaware?
• What are the bureaucratic/cultural/cost barriers to fixing it?
• Is there some technicality that means they can’t show the correct calculation?
• Is it deliberate? Are they profiting from the resulting mistake?

Here’s my guess: there’s a stakeholder somewhere in the chain who believes that its the user’s job to know all of the little details about tax, including how to calculate. But here’s the rub: this screen actively misleads a user, as opposed to just leaving them to calculate on their own.

It would be better to show less, or nothing, forcing a user to to check with their accountant, or perhaps re-read how to do the calculation. But I’d prefer it if they showed the right number!