For most people that’s not a problem in the UK. Partly that’s because all employed income has to be reported to HMRC by your employer, and party we just don’t have the same system of tax deductions - you can’t write off charity donations, and expenses are only deductible by companies. For children you have to register for child benefit payments with the government.

Even for the self employed it’s generally a pretty simple process of filling in your income and expenses and then everything else is calculated for you.