Q. Shouldn't the taxes only be calculated on what he actually earned from his Missouri employer?
A. Yes.
Q. So why is Missouri calculating taxes on all that?
A. MO, like most other states, starts with you federal Adjusted Gross Income. But, it only appears like they are taxing all your income. TurboTax (TT) will calculate MO tax on ALL your income. But then it will apply a percentage (calculated on form MO-NRI based on the ratio of your MO income to the total. TT will do all this when you indicate that you and your spouse are non residents.
