[emdowling]

In the UK, it is like this for the vast majority of tax payers. Certain criteria, like earning over £100k, mean you need to file a return. The government will usually send you a letter informing you that you've met the criteria too, as they know how much you earn each month.

At any time, you can log in and easily see how much the government thinks you have earned and from who, and which tax rate (tax code) is being applied to you. You can correct this as well if it is wrong.

Having lived in Australia, the US and UK, I've found the UK system to be the easiest to understand and navigate. Australia isn't too far behind. The US is just a mess.