Do you get any kind of deduction for giving to non-profits/charities? I give about 12-15% of my gross income to non-profits/charities every year and get a generous tax deduction for doing so. The other thing that tends to be complicated with my taxes is selling stocks. How does the UK handle things like that?
People don't tend to invest so much in stocks, instead settling for other instruments, like ISAs that already handle the tax end of things (https://en.wikipedia.org/wiki/Individual_Savings_Account). ISAs are an attempt by the UK government to encourage saving / investment by providing tax incentives to do so. Again, tax considerations done upfront vs after-the-fact.
If you do invest in stocks, you're liable for capital gains tax, just like in the US, but whether you need to file or not is dependent on how much you actually made.
If you make too much, you'll have to file taxes yourself, but it's relatively straightforward.
The point is not that the system is perfect, but that it handles the case for probably >90% of the population, without stress or complications for them.
It depends how you donate, but for payments direct from payroll (if your employer supports it) you essentially pay out of your pretax income.
For cash gifts the charity can claim back 25p in the £ on your gift. For property, land and shares you deduct it against your tax payments at the end of the tax year and claim for a refund.
In the UK people tend not to own stocks directly but through one of the various investment "wrappers" such as the ISA (individual savings account), which are tax-free for up to £15k/year investment paid in.
Stocks shouldn't be complicated; you've got a cost basis, a date of acquisition, a date of disposition and a final sale price. Withhold based on the deltas and you're all set right?
ESPP are complicated for me because my company withholds the taxes already, but that isn't reflected in the form I get from the stock company so I have to spend significant time every year refiguring out how to adjust and report everything while cursing myself for not taking notes the previous year.
