Loan Refinance Interest Deduction: What to Know

This refinance calculator estimates a new loan’s monthly payment and total interest from the amount refinanced, APR, and term. “Loan refinance interest deduction” can also refer to whether interest is tax-deductible; this calculator does not determine tax treatment, which depends on applicable rules and your circumstances.

Formula

The calculator uses the standard fixed-rate, level-payment amortization formula. First, it calculates the monthly payment, rounds that payment to cents, and then estimates total interest using that rounded payment:

• Monthly payment: PMT = round(P × r / [1 − (1 + r)⁻ⁿ], 2)
• Total interest: I = PMT × n − P

P is the amount refinanced in dollars; APR is the annual percentage rate entered as a percentage; r is the monthly rate, APR ÷ 1200; n is the number of monthly payments, term in years × 12; PMT is the rounded monthly payment in dollars; and I is estimated total interest in dollars over the full term. The calculator assumes the stated APR is a nominal annual rate divided into monthly periods.

Worked Example

Using the defaults—$20,000, an 8% APR, and a five-year term:

1. Convert the APR to a monthly rate: r = 8 ÷ 1200 = 0.0066667.
2. Convert the term to payments: n = 5 × 12 = 60.
3. Calculate the payment: PMT = round(20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰], 2) = $405.53 per month.
4. Calculate interest using that rounded payment: I = $405.53 × 60 − $20,000 = $4,331.80.

Assumptions

• The APR stays fixed for the full term.
• Payments are equal, made monthly, and begin on the schedule assumed by a standard amortization calculation.
• Interest accrues monthly at APR ÷ 12.
• The estimate excludes lender fees, taxes, insurance, mortgage insurance, escrow, and other charges because none is entered.

What a Refinance Interest Deduction Means

A refinance replaces an existing loan with a new loan. The new loan may have a different balance, APR, payment schedule, or term. The calculator describes the new loan’s basic payment and interest arithmetic; it does not establish whether any interest qualifies for a deduction on a tax return.

That distinction matters because “interest paid” and “deductible interest” are not interchangeable. A loan statement may show interest charged or paid, but tax treatment can depend on the type and use of the borrowing, the property or expense involved, the borrower’s circumstances, documentation, and the rules that apply to the relevant tax year and jurisdiction. Refinancing can change details that matter to those rules. No general calculator based only on loan amount, APR, and term can resolve those questions.

For an individual tax question, consult current official tax guidance or a qualified tax professional. Keep the closing or loan documents and annual interest statements; they can help a tax professional assess the facts. Do not treat the calculator’s total-interest output as a deductible amount.

How to Compare the New Loan’s Costs

A lower monthly payment alone does not show whether a refinance reduces total borrowing cost. A longer repayment period can lower the payment while increasing the time interest accrues. For a meaningful comparison, gather the current loan’s remaining balance, remaining term, APR, and payment, along with the proposed loan’s principal, APR, term, and itemized charges. Compare periods that make sense for your situation and account for any fees separately; this calculator does not include them.

For example, the default calculation produces a $405.53 payment and $4,331.80 in interest over 60 months. If the same principal and APR were repaid over a longer term, the monthly payment would generally be lower, but more payments would be made and total interest could be higher. If the proposed loan includes fees added to the balance, the amount borrowed—and therefore the estimate—would also rise. These are arithmetic effects, not a recommendation about whether to refinance.

Inputs, Costs, and Common Calculation Limits

• Use the correct principal: Enter the amount being borrowed under the new loan, not automatically the original loan amount. If costs are financed, include them only if they are part of the new balance.
• Use the APR requested by the lender: Enter it as a percent, such as 8 for 8%, not 0.08. If a lender provides a rate and a separate APR, check which figure the calculator asks for.
• Convert the term correctly: The input is years. A 30-month term is 2.5 years; a 60-month term is five years.
• Account for rounding: Payments are rounded to cents, and total interest uses the rounded monthly payment. Actual final payments can differ slightly because lenders apply their own payment dates and rounding practices.
• Separate loan interest from other costs: Fees, prepaid items, insurance, and taxes are not included in the interest result. Request an itemized estimate and review the loan documents for the figures that apply.

The formula assumes regular payments and a constant rate. It does not model variable rates, irregular payment dates, skipped or extra payments, payoff quotes, late charges, or changes in the balance. It also does not calculate tax deductions, compare tax outcomes, or determine eligibility for any tax treatment. Its purpose is limited to estimating scheduled payments and interest under the stated assumptions.

Frequently Asked Questions

Is refinance loan interest tax-deductible?
There is no answer that applies to every refinance. Tax treatment depends on applicable rules and details such as the loan and how funds are used. The payment calculator does not determine deductibility; check current official guidance or ask a qualified tax professional.

Does refinancing automatically make interest deductible?
No general conclusion follows just from replacing a loan. A refinance changes a loan’s terms, but whether interest receives any tax treatment depends on the relevant rules and facts, not the word “refinance” alone.

Does this calculator show how much interest I can deduct?
No. It estimates total scheduled interest from principal, APR, and term. Deductible interest, if any, may not equal that total, and this tool does not evaluate tax rules or personal circumstances.

Why can a lower payment lead to more total interest?
A longer term spreads repayment over more months. Even when each payment is smaller, interest may accrue for longer; compare total payments and costs as well as the monthly amount.

Should I include refinance fees in the loan amount?
Only include fees if they are financed into the new principal. Fees paid separately are not represented in this calculation, so review them separately when evaluating the overall cost.

This result is an estimate; the lender’s disclosure gives the exact figures.

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• Loan Balance Amortization Calculator: See What You Owe
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in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2