I am trying to build a spreadsheet for client use that takes a given income, in a given month and applies the appropriate marginal rate to that month.

For example, Jan income in column A would show pretax deductions, state tax, FICA tax and then Federal tax.

I would like the income, say 10k in Jan taxed at 10% and then the next months income say 13k, Column B, taxed at the proportionate 10% up to 17,700, with the remaining amount taxed at the next marginal rate of 15%.

I would like to continue this progressive calc throughout the year, adding additional variable income per month that is taxed at the appropriate marginal level.

Thanks!