Middle-Class Savings and Investment Act This bill provides tax incentives for savings and investment for middle-income taxpayers. Specifically, it (1) increases the current tax bracket for capital gains and dividends; (2) allows an exclusion from gross income for up to $300 of interest income received by a taxpayer; (3) increases the threshold for the net investment tax for married couples filing jointly to $400,000, adjusted for inflation (thus eliminating the tax effect known as the marriage penalty); and (4) increases the maximum contribution amount and the rate of the saver's tax credit. As an offset to the cost of these incentives, the bill extends through 2028 the limitation on the deduction for state and local taxes.