In a proportional system it could be like this. 50 dollar deductible. First 1000 dollars is taxed by 10%, 1001 to 5000 is taxed 20% and anything over 5000 is taxed by 30%.
Person 1 earns 10 dollars a year but since there is a 50 dollar a year deductible he will pay no tax. 10 dollars to live on.
Person 2 earns 100 dollars a year, has a 50 dollar deductible leaving only the 50 dollars to be taxed by 10% which is a tax of 5 dollars. That gives 95 dollars to live on.
Person 3 earns 10000 dollars a year, has a 50 dollar deductible. the 10000 dollars are taxed the following. The first 1000 by 10% which is 100 dollars, then next 4000 is taxed by 20% which is 800 dollars and the remaining income of 5000 dollars is taxed by 30% which is 1500 dollars. This is a grand total of 2350 dollars in tax (with the 50 dollar deductible.. even though it dont matter jack for this person). That will leave the person 7650 dollars to live off.. ohh poor rich people have less to live off.. boo hoo... will have to skip one weekly botox treatment.