This is your marginal tax rate, the rate at which each additional dollar of income will be taxed. If you pay only Federal income taxes, it is the highest tax bracket you used when you calculated your taxes. Federal tax brackets currently are: 10%, 15%, 25%, 28%, 33%, and 35%. If you also pay state and/or local income taxes, these marginal rates can be added to the Federal rate. For example, if you had to pay 25% to the IRS and 5% to the state of Pennsylvania, your tax bracket is 30%. To perform a "pre-tax" analysis enter zero (0) as the tax rate.The period cannot exceed the shortest mortgage term. The period may be stated in fractions. For example, 25 years and 1 month would be entered as 25.083, 25 years and two months would be 25.167, and 25 years and 3 months would be 25.25, etc.This affects the after-tax analysis because on a purchase transaction points are fully deductible in the first year whereas on a refinance the deduction must be spread over the life of the loan.This is the interest rate you could earn on the monies you spend during the period you are in your home. For most people, it would be the interest rate on a bank account or a money market fund. In after-tax cost comparisons, this figure is adjusted to an after-tax basis.