The UK taxes are, in all fairness, the simplest I have ever seen (and I've made a point of learning about and comparing several countries). You can use a calculator such as Listen To Taxman [0] and be within a 1% error margin from the reality.

Of course, there are always edge cases, and the government has deliberately made some areas a mess (case in point: contractors); but the base use case of standard salary is insanely simple. And, for our American friends, the NHS is included.

[0] https://listentotaxman.com/