The Missouri income tax form is pretty easy to fill out once you have calculated your federal taxes, because the Missouri form uses numbers from the federal 1040. In Missouri, both U.S. residents and nonresidents use the same forms. If you are single or married with one income, you can probably use the MO-1040A. There is a longer MO-1040 form that married couples with two incomes must use. Nonresidents, keep in mind that when the questions refer you to specific line numbers on the federal tax returns, they mean the 1040 form for residents. Nonresidents will have to pay attention to the content of the question; i.e., which dollar amount from the federal return is being asked for (for example, the “Wages” line). Use common sense.
If you lived/worked in two states during the year, you will likely need to fill out a tax form for each state. For Missouri, part-year residents should use form MO-NRI (to determine what part of your income was earned in Missouri) and form MO-CR (to get a tax credit for money paid in taxes in another state).
The State of Missouri website has a Form Selector that will help you determine which forms you need to use. Also on the website are forms that let you type in the values and automatically complete the calculations. Tax forms for other states can be found by searching their individual department of revenue websites.