$5T
Where does this number come from? In 2021 the govt collected $2.04T in income taxes.
So 42% rate?
Assuming an average household income of $97,026 (as it was in 2019) and 125M households;
To replace income tax revenue with a flat tax would mean a 17 percent flat tax.
If you are trying to replace all federal revenues ($4.03T in 2021), it would require a flat tax of 33 percent. This would come together with repealing the payroll tax, business income tax, death tax etc...