I moved to the UK last year from the US. Over here, you only file your own taxes if your income is over 100k GBP -- which is probably a reasonably simple proxy

I moved to the UK last year from the US. Over here, you only file your own taxes if your income is over 100k GBP -- which is probably a reasonably simple proxy for "your tax situation might be more complicated." No doubt it has edge cases, but it's a nice sorting mechanism for the majority of cases.