I've been slowly trying to build a spreadsheet that calculates overall marginal tax rates for different types of income. This would be very useful in ER as one needs to be able to calculate how much roth conversion to do, whether and when to harvest capital gains (and losses), etc.
This project is difficult because there are so many intersecting tax policies. You have social security/FICA tax (which can be a form of saving if you discount for risk that SS won't be there when you are old), federal income tax, state income tax, different rates for dividends/capital gains, obamacare subsidy (which is treated via federal taxes), etc.
Does anyone know if such a spreadsheet exists? Alternatively, is anyone interested in crowd-creating such a document?