I would like to know how a flat tax is regressive? Most proposals exclude a certain amount of income automatically making it progressive.

Let’s say we had a 20% tax on all income over 50K.

Family A – 60K
Taxable income – 10k
Tax Paid – 10k*20% = 2K
Income Tax % – $2k/60K = 3.33%

Family B – 80K
Taxable Income – 30K
Tax Paid – $30k*20% = 6K
Income Tax % – 6k/80k = 7.5%

Family C – 150K
Taxable Income – 100K
Tax Paid – $100k*20% = 20k
Income Tax % – 20K/150K = 13.3%