system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a flat tax favor the wealthy?
gpt
Lets say rich guy makes $1,000,000 a year, and poor guy makes $25,000, and then lets assume a 10% flat income tax rate. Rich guy will pay $100,000, which is much more than poor guy's $2,500. Rich guy, however, is still left with $900,000 which is presumably more than enough to cover his necessary expenses plus a good amount of luxuries. Poor guy has $22,500 left, which might not cover all of his necessary expenses. That $2,500 that poor guy pays in taxes has a more substantial effect on his quality of life than the $100,000 that rich guy paid because at that income level virtually every dollar he gets goes to sustaining his home, food, medical insurance, etc. Rich guy on the other hand still has more than enough left over after taxes to buy not only what he needs but most of what he wants, and every extra dollar he receives would most likely go to savings and investments rather than subsistence.

Edit: Also, in the specific case of the US, many of the flat tax proposals that have been made would lower the current tax rate for those in the upper tax brackets and offset it by raising the tax rate for those in lower tax brackets. Also, capital gains (income made from capital investments), is generally taxed at a lower rate than normal income, and that is how a good portion of the income of the wealthy is generated. The poor/working class on the other hand generally don't make enough money to make capital investments and therefore can't benefit from the lower tax rate of capital gains.