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Mortgage Interest Cap Calculator
The Tax Cuts and Jobs Act capped mortgage interest deduction at $750K of acquisition debt for loans originated after December 15, 2017 ($1M legacy cap for older loans). Married filing separately gets half the cap. Interest on debt above the cap is non-deductible. This calculator computes the pro-rata deductible interest and lost deduction.
Deductible interest
$45,882
Non-deductible interest
$6,118
Applicable debt cap
$750,000
Debt above cap
$100,000
How the math works
Mortgage interest deduction caps debt at $750K (post-12/15/2017 originations) or $1M legacy. MFS gets half the cap. Interest on debt above the cap is non-deductible. Limit applies to total acquisition debt across primary and one second home.
HELOC and home equity loans qualify for deduction only if used to substantially improve the home. Cash-out refi proceeds used for non-home purposes are not deductible.
EveryCalc calculators are designed for fast, practical estimates with transparent inputs and no required account. We use plain formulas, visible assumptions, and related tools so visitors can check the result from more than one angle.
Results are informational only. For financial, tax, legal, medical, construction, or other high-impact decisions, verify the output against primary sources or a qualified professional.
Learn more about our review process on the EveryCalc methodology page.
How this calculator works
What this page estimates
This Mortgage Interest Cap Calculator is built to give a quick, browser-based estimate for mortgage interest cap. The Tax Cuts and Jobs Act capped mortgage interest deduction at $750K of acquisition debt for loans originated after December 15, 2017 ($1M legacy cap for older loans). Married filing separately gets half the cap. Interest on debt above the cap is non-deductible. This calculator computes the pro-rata deductible interest and lost deduction. The inputs stay on the page during normal use, and the result should be treated as an estimate for planning, comparison, or education rather than professional advice.
Calculation approach
The calculator applies the standard relationship implied by the inputs, then formats the answer so it can be checked and reused. For finance tools, the most important step is using consistent units, rates, time periods, and assumptions before comparing the result with another calculator or outside quote.
Example workflow
For example, start with a realistic value you already know, change one input at a time, and watch how the answer moves. That makes it easier to tell whether the result is being driven by the main amount, the rate, the time period, or a unit conversion.
Practical checks
- Use current, real-world numbers when the result affects money, health, tax, or legal decisions.
- Run a low, base, and high case when the inputs are estimates.
- Check the related calculators below when the next decision depends on a different assumption.
How to interpret the mortgage interest cap result
Best use
Use the result as a planning number for comparing payments, rates, returns, tax reserves, or cash-flow choices before you request a quote or make a commitment.
Cross-check
Compare the answer with the contract, lender estimate, tax form, brokerage statement, payroll record, or invoice that will control the real-world outcome.
Watch for
Do not rely on a single optimistic rate, return, or fee assumption. Money pages work best when you run low, base, and high cases and keep professional advice separate from the estimate.
This page belongs to the Finance calculator library, so the answer should be read in the context of the decision you are modeling rather than as a universal rule.
Before relying on this mortgage interest cap estimate
Most calculator mistakes come from the inputs, not the arithmetic. Use this short audit before you reuse the answer in a spreadsheet, quote, application, or important conversation.
Confirm source numbers
Match balances, rates, fees, taxes, income, and payment dates against the lender quote, payroll record, tax form, statement, invoice, or contract.
Separate cash flow from total cost
A lower monthly payment can still cost more over time if fees, interest, taxes, or a longer term are hidden in the structure.
Run conservative cases
Test at least one higher-cost or lower-return case before using the output for a purchase, refinance, investment, loan, or tax decision.
Rerun this page when the rate, price, term, fee, tax rule, income, expense, or expected holding period changes.
How to Use
- Enter total acquisition mortgage debt (across primary and one second home).
- Indicate origination date (post-12/15/2017 = $750K cap).
- Enter filing status.
- Enter annual mortgage interest paid.
- Read deductible vs non-deductible interest.
Frequently Asked Questions
Can I have two mortgages?
Yes — primary and one second home count together against the cap. Investment property mortgages have no cap (full deductibility on Schedule E).
HELOC deductibility?
Only if used to 'substantially improve' the home (acquisition indebtedness). HELOC for college, cars, vacation = not deductible after TCJA.
TCJA expiration?
Current rules expire after 2025 — could revert to $1M cap if not extended. Watch tax legislation in 2025 for changes.
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