A capital gain occurs when you sell a capital asset such as a stocks or real estate for more than you paid for it. Missouri tax law requires you to pay a state capital gains tax in the year you realized the capital gain. Unlike the Internal Revenue Service, however, the state of Missouri does not differentiate between long-term and short-term capital gains. Therefore, you will pay the same Missouri capital gains tax regardless of the length of time you held the asset prior to sale.
Add all individual capital gains to determine your total capital gain for the tax year. For example, assume your total capital gain for the tax year is $20,000.
Find out the Missouri capital gains tax rate for the tax year for which you are filing. For 2011, the Missouri capital gains tax rate is 6 percent.
Multiply your total capital gain by the Missouri capital gain tax rate expressed as a percent. Continuing the same example, $20,000 x .06 = $1,200. This figure represents your Missouri capital gains tax liability for the current tax year.