The majority of tax payers actually don’t have very complex taxes, if you only have w-2 income and don’t itemize deductions, you just need the single page 1040. Even small businesses aren’t complicated if they have proper bookkeeping, or if you’re just deducting mortgage interest. The piles of tax regulations really are for wealthy people and corporations with complicated accounting.

Here in NZ we got rid of almost ALL deductions the tax system is so simple that almost all people with one job pay exactly the right tax through employer PAYE (as someone who runs a small company I do my PAYE with 1 line of spreadsheet formulae, it's easy).

This means most people don't need to file, if you want to it's a 1-2 page web form, and, starting last year, the IRD will do it for you anyway and directly credit your refund (with interest) to your bank account without you asking

What do you do about interest on savings accounts or capital gains on stocks?

The bank takes it out at a standard rate - when you open an account you tell them your marginal rate, if you get it wrong it's obvious to the IRD.

We have no tax on capital gains (we should, it badly distorts our markets, leaves too much money in real-estate).

Was that the 9-9-9 plan? To be honest such simple tax rules was eye-opening and refreshing but I don't think it was particularly fair.

It actually goes back to the flat tax proposals to set the top rate to 28% with very few deductions.

The idea was that you don’t have some rich paying the top rate of 39%, and some paying near zero (cough, cough, Mr. Trump) due to a large discrepancies in deductions.

You'll notice they never specified how big the writing was going to be.