What is being compared
A deduction reduces taxable income; it is not a dollar-for-dollar reimbursement of mortgage interest. This calculator makes that distinction visible by showing eligible interest separately from the estimated tax reduction.
Formula and timing
Eligible deduction is min(interest paid, eligible limit). Estimated tax reduction equals eligible deduction × marginal rate ÷ 100. The formula intentionally does not call the $10,000 a saving; it is a reduction of taxable income.
Worked example with the displayed units
With $12,000 paid, a $10,000 eligible limit, and 22%, the deduction is $10,000 and the estimated reduction is $2,200. The remaining $2,000 is displayed as above the entered limit.
When to use this result
Use this as a worksheet after obtaining an annual mortgage-interest statement and after identifying whether itemizing produces an incremental deduction. Compare the tax outcome with and without the itemized amount.
Costs and conditions outside the fields
Jurisdiction, filing status, statutory caps, credits, income phase-outs, and the standard deduction are not calculated. The browser cannot determine whether an amount is incremental to deductions otherwise claimed.
Mistakes that change the answer
Do not enter a monthly payment as annual interest; use the interest amount from the statement. A marginal rate is not an effective overall tax rate, and 22% is entered as 22, not 0.22.
Scope of this page
This page estimates the tax consequence of an interest deduction. An amortization schedule separates principal and interest in a payment, but it does not test tax eligibility. It is educational information, not tax or legal advice.
Itemizing is the missing comparison
The entered interest limit is not a finding that itemizing saves tax. A deduction changes a return only to the extent that itemized deductions exceed the alternative deduction available to the filer. For example, an extra $10,000 of eligible interest may not create a $2,200 reduction at a 22% marginal rate if other deductions already make the alternative larger, or if only part of the interest increases the itemized total. Keep the annual statement, the other itemized amounts, filing status, and the relevant tax-year rule together before using this estimate. The result is most useful as one line in that comparison, not as a reason to borrow more or to assume a payment is subsidized.
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