Home Equity Financing Methodology

Primary sources

Home equity loan and HELOC interest deductibility is governed by IRC §163(h) and the Tax Cuts and Jobs Act of 2017 (TCJA), which limited deductibility to loans used to 'buy, build, or substantially improve' the taxpayer's primary or secondary residence (26 USC §163(h)(3)(B)(ii)). IRS Publication 936 provides the practitioner guidance for this limitation.

HELOC and home equity loan disclosure requirements follow Regulation Z (Truth in Lending) for open-end and closed-end credit respectively. CFPB's HELOC guide provides the required APR, margin, index, and annual cap disclosure formats we reference for our rate inputs.

Product comparison framework

Three products modeled: (1) HELOC — variable rate (Prime + margin), interest-only draw period, principal+interest repayment period, revolving (draw as needed). (2) Home equity loan — fixed rate, fixed term, lump sum disbursement, immediate P+I payments. (3) Cash-out refinance — replaces existing mortgage with larger new mortgage, fixed rate, 30-year term.

Total interest cost: HELOC = sum of monthly interest accruals during draw + amortized P+I during repayment. HEL = standard amortization formula. Cash-out refi = (new mortgage total interest) - (old mortgage remaining interest) = incremental interest cost of the cash-out. We compute all three and present side-by-side.

Tax deductibility

Post-TCJA, home equity interest is deductible if the loan proceeds are used for 'buy, build, or substantially improve' the home. Renovation projects clearly qualify. The $750,000 combined acquisition and home equity debt limit (TCJA change from $1M) applies to the total outstanding mortgage + HELOC/HEL. Our calculator flags when the combined balance approaches this limit.

After-tax cost = before-tax rate × (1 - marginal_tax_rate) for the deductible portion. We compute both before-tax and after-tax rates assuming the user is itemizing deductions (if not itemizing, the deductibility benefit disappears entirely).

Limitations

HELOC rates are variable — our model shows rate sensitivity at ±2% Prime changes. Closing costs (2-5% of loan amount for cash-out refi, 1-3% for HEL, often minimal for HELOC) significantly affect the true cost for short holding periods. Cash-out refi is a poor choice if your existing mortgage rate is below current market rates — we flag this break-even prominently.

Update protocol

This category is reviewed quarterly. Immediate updates are triggered by changes to the primary source documents listed in the citations above — rate table revisions, new agency guidance, or regulatory amendments.

Error reports go to info@bedrockatools.com. Corrections are published on our corrections page.