(2) Medicare likewise is 2.9%, not 1.45%.

(3) To be more precise, if you “earn” $100, you really earn $107.65 because your income should include taxes paid by the employer. Tax rates on this total income would be lower. (eg. 10% tax rate on income would actually be 10/107.65 rate on total income)

(4) It is highly misleading and inaccurate imho to call Social Security regressive. Social Security is a flat tax up until an income where benefits stop accruing. Furthermore, the accrual of benefits is highly PROGRESSIVE! Low income and short career people get a GREAT deal from Social Security. Higher income people and long career people get a terrible deal. And for the super rich, Social Security is somewhat irrelevant.

I think the right way to think about it (difficult to calculate… requires assumptions) is to ask what is marginal Social Security tax rate vs. marginal increase in present value of Social Security benefits. What you’ll find is that Social Security is highly progressive until maximum taxable earnings is reached, then it becomes briefly regressive (as tax rate goes to zero), then it becomes a flat tax of zero (zero tax, zero increase in benefits).