A marginal tax rate is the rate at which an individual or business is taxed on their last dollar of income. In other words, it is the tax rate that applies to the highest tax bracket that an individual or business falls into.

Marginal tax rates are used in progressive tax systems, in which tax rates increase as the amount of income increases. For example, if an individual's marginal tax rate is 25%, this means that the individual will pay 25% in tax on their last dollar of income.

Marginal tax rates are important to consider when making financial decisions, as they can affect the amount of tax that an individual or business pays on their income. For example, if an individual is in a high marginal tax bracket, they may be more inclined to invest in tax-deferred retirement accounts or to take advantage of tax deductions and credits to reduce their tax burden.

If you are interested in understanding your marginal tax rate and how it may affect your financial decisions, it is a good idea to seek advice from a tax professional or from the tax authority in your jurisdiction.