Loan Interest Tax Calculator

Calculator Inputs

Enter your loan details, expected deductible share, and estimated tax rate. The calculator will project annual interest, tax relief, and after-tax borrowing cost.

Loan Amount

Annual Interest Rate (%)

Loan Term (Years)

Payments Per Year

Extra Payment Per Period

Deductible Interest (%)

Marginal Tax Rate (%)

Schedule Start Year

Loan Use Note

This tool provides planning estimates only. Deductibility rules vary by country, loan purpose, income limits, filing method, and changing tax regulations.

Example Data Table

This example shows how annual balances, interest, and tax savings can change over time for a fixed-rate amortizing loan.

Year	Total Payments	Interest	Principal	Deductible Interest	Tax Savings	Ending Balance
2026	$24,910.15	$9,960.08	$14,950.07	$7,470.06	$1,643.41	$165,049.93
2027	$24,910.15	$9,077.43	$15,832.72	$6,808.08	$1,497.78	$149,217.22
2028	$24,910.15	$8,142.67	$16,767.48	$6,107.01	$1,343.54	$132,449.74
2029	$24,910.15	$7,152.72	$17,757.43	$5,364.54	$1,180.20	$114,692.31
2030	$24,910.15	$6,104.33	$18,805.82	$4,578.25	$1,007.21	$95,886.49

Example assumptions: $180,000 loan, 5.75% annual rate, 10 years, monthly payments, $100 extra payment, 75% deductible interest, and 22% marginal tax rate.

Formula Used

The calculator uses a standard amortized loan payment formula and then estimates tax benefit from the deductible interest share.

Periodic Rate: Annual Interest Rate ÷ Payments Per Year
Scheduled Payment: P × [r ÷ (1 − (1 + r)⁻ⁿ)]
Interest Each Period: Current Balance × Periodic Rate
Principal Each Period: Payment − Interest
Deductible Interest: Interest × Deductible Percentage
Estimated Tax Savings: Deductible Interest × Marginal Tax Rate
After-Tax Interest Cost: Interest − Estimated Tax Savings
After-Tax Total Cost: Principal Repaid + After-Tax Interest Cost

How to Use This Calculator

Enter the original loan amount.
Add the annual interest rate and full loan term.
Select how often you make payments.
Include any extra payment planned each period.
Enter the share of interest you expect to deduct.
Add your estimated marginal tax rate.
Choose the schedule start year for yearly grouping.
Press Calculate Tax Impact to view results.
Review the summary cards, yearly table, and chart.
Download the summary using CSV or PDF buttons.

Frequently Asked Questions

1. What does this calculator actually estimate?

It estimates your payment schedule, yearly interest, deductible interest, possible tax savings, and after-tax borrowing cost. It is best for planning, not for preparing a final return.

2. Is every loan interest payment tax deductible?

No. Deductibility depends on loan purpose and local rules. Some mortgage, business, rental, and student loan interest may qualify, while many personal loans do not.

3. Why do I need both deductible percentage and tax rate?

The deductible percentage estimates how much interest qualifies. The tax rate estimates the value of that deduction. Together, they convert deductible interest into possible tax savings.

4. Does an extra payment change the tax result?

Yes. Extra payments reduce balance faster, which lowers future interest. Lower interest can reduce total deductions, but it usually cuts total borrowing cost more strongly.

5. Can I use this for mortgages or business loans?

Yes, as a planning estimate. Adjust the deductible percentage based on the portion you believe qualifies. Confirm final treatment with a tax professional or current local guidance.

6. Why does the chart use yearly values instead of every payment?

Yearly values are easier to review for tax planning. They show how balances and tax savings evolve over time without making the chart overcrowded.

7. What does after-tax interest cost mean?

It means your estimated interest expense after subtracting projected tax savings from deductible interest. It helps compare the real cost of borrowing more clearly.

8. Should I rely on this result for filing taxes?

Use it for planning only. Filing requires current tax law, supporting documents, deduction limits, and sometimes detailed allocation rules that this estimator does not replace.