I'm not the guy you're responding to, but I thought I had a reasonable strategy to simply calculate it. I can't do it for America, because I'm not sufficiently familiar with what data you have available and am instead going to do the analysis for Sweden.

In Sweden the labour share of GDP is 55%, however taxes on wages are 60% of the total government income, and a large remaining fraction of the taxes on work income. Another 30% is from VAT. Let's assume arbitrarily that half the VAT is paid by workers and not with income from capital.

Under this assumption, workers receive 55% of GDP in compensation before taxes, but pay 70% of all taxes.

If taxes on income were the same for workers as for capital then workers would pay 55% instead of 70%, so taxes would be 18% lower than they are now.

Its difficult to define terms like ultra rich and middle income earner, but my guess is that if you increased the top marginal tax rates such that rate on the "ultra rich" was something like 70% (including capital gains, etc), you could completely eliminate taxes for the bottom 50%.

The top 1% earners earned 21% of all U.S. income while paying 40% of all federal income taxes [0]. I would guess going from 50% to 70% would increase that share to would increase that percentage to 58%.

[0]: https://www.heritage.org/taxes/commentary/1-chart-how-much-t...

Old comment here, but I was assuming not just income tax to increase, but also to have capital gains, dividends, etc to be taxed at 70%. Current cap there is 20%, per my understanding, and a substantial amount of wealthy person's income is taxed at these favorable rates.

Can you show how you calculated that?