Begin with your MA return. For any income from sources besides your wages that were not sourced in MA, be sure to exclude them from your MA tax return by selecting Not Massachusetts sourced. In the Income Adjustments screen, enter your income earned from your new job but prior to your move in the Massachusetts Income While Nonresident field. Enter the income earned while you lived in Massachusetts from August through December in the Massachusetts Income While Resident field. Do not enter the income from your other job in January anywhere. On the Your Massachusetts Bottom Line screen, take note of Income Tax under Taxes and Credits. You will need this later.
In MO, select Part-Year Resident Filing as a Resident as Your Missouri Resident Status. When you get to the Out of State Tax Credit, select Massachusetts. Only enter the income that you earned while living in Missouri that was also taxed by Massachusetts, the amount you earned from your new job from January through August. To determine how much that was, you can either look at old pay stubs, or determine it by multiplying your total income by the fraction of the time that was earned while living in Missouri. So if you earned $50,000 for the year from the new job and were in Missouri for about 2/3 of that time, you would enter $50000*2/3 or $33,333.
For the income tax paid to Massachusetts, you want to enter the tax you paid to MA solely on that income. On the Your Massachusetts Bottom Line summary screen, TurboTax lets you know how much income tax you owe to Massachusetts. Once again, if 2/3 of that amount was earned in Missouri, then you would enter 2/3 in the Income Tax field. If MA taxes $2,100 on the $50,000 then you would enter $1,400, 2/3 of the tax MA imposed. This will correctly apply the credit to the amount you owe Missouri.
