- Tax-deductible interest
- Interest the tax code lets you subtract from taxable income. Mortgage interest, qualifying home-equity interest, student-loan interest and business interest may qualify; interest on personal loans, auto loans and credit cards generally does not. This calculator assumes all the interest you enter is deductible, so check that your loan qualifies before relying on the result.
- Marginal tax rate
- The rate applied to your last dollar of taxable income, here meant as your federal and state rates combined. A deduction removes income from the top of your income, so each deductible dollar of interest saves tax at this rate. At a 22% marginal rate, $1,000 of deductible interest trims your tax bill by about $220.
- Tax savings
- The reduction in income tax that comes from deducting loan interest, calculated as deductible interest multiplied by your marginal tax rate. It lowers the after-tax cost of borrowing but never makes borrowing free: you still pay the full interest to the lender and recover only a fraction of it through a smaller tax bill.
- Itemized deductions
- Specific expenses, such as qualifying interest, state and local taxes and charitable gifts, listed individually on your federal return instead of taking the standard deduction. Most interest deductions help only if you itemize and your itemized total exceeds the standard deduction. Student-loan and business interest are exceptions, since they are claimed separately.
- Standard deduction
- A flat amount, set each year by the IRS and based on filing status, that you may subtract from income instead of itemizing. If your itemized deductions, including loan interest, do not exceed it, deducting the interest produces no extra savings. This calculator does not check that comparison, so its savings figure is an upper estimate.
- Student loan interest deduction
- A deduction for interest paid on qualified education loans, capped at $2,500 a year (IRS, 2026, as stated in this calculator’s disclaimer). It is taken as an adjustment to income, so you can claim it without itemizing, although it phases out at higher incomes. Interest above the cap is not deductible, which this estimate does not enforce.
- Interest rate
- The annual percentage the lender charges on the unpaid balance of the loan or credit line. The calculator applies it monthly to the declining balance to find each year’s interest. A higher rate produces more interest, and therefore a larger deduction, but the added interest always costs more than the tax it saves.
- First-year interest
- The total interest paid during the first twelve payments. On an amortizing loan the balance is highest at the start, so this is usually the largest annual interest figure and the largest annual tax saving. Interest, and the deduction with it, shrinks each year as principal is repaid, which is why the average annual saving is lower.
- Loan term
- The number of years over which the loan is scheduled to be repaid in equal payments. A longer term lowers each payment but keeps the balance outstanding longer, so total interest rises. In this calculator a longer term also spreads the deduction over more years, raising total tax savings while the total interest cost grows faster.
