The marginal tax rate is the tax rate you need to pay on every additional dollar included in your taxable income. Usually, it is equal to your highest tax bracket. Here is an example to help you understand it better. Let us assume that you are a single filer with a taxable income of $30,000. According to the Federal tax rates, you would fall into the 12% tax bracket. Now, in case your taxable income is increased by $1, you will need to pay a 12% tax on that additional dollar of your income. Now, let us assume your taxable income was $41,000. In this case, most of your income will fall within the original 12% tax bracket only. But, the last few hundred dollars will still fall into the 22% tax bracket. Therefore,  your marginal income tax rate will be 22%.