HELOC Calculator
Calculate your Home Equity Line of Credit payments instantly. Enter loan amount, rate, and draw period to see monthly costs and total interest.
HELOCs operate in two phases. In the Draw Period, payments are typically interest-only. In the Repayment Period, you must pay back principal and interest, causing a massive payment shock. Budget accordingly!
Capital Hydraulics & Mathematical Formulations
CLTV underwriting boundaries, interest-only draw mechanics, and recast amortization equations
A Home Equity Line of Credit (HELOC) is an open-end revolving second mortgage secured by the borrower’s real estate asset. Unlike a conventional installment mortgage, a HELOC operates with dual-phase lifecycle hydraulics: an initial Draw Period (typically 5 to 10 years) followed by a mandatory Repayment Period (typically 10 to 20 years).
Combined Loan-to-Value (CLTV) Underwriting Limit
Lenders constrain second lien risk exposure by capping total residential indebtedness relative to appraised collateral market value. The Combined Loan-to-Value (CLTV) equation governs the maximum allowable credit line ceiling:
For example, if a primary residence appraises at $500,000, the lender establishes an 80% maximum CLTV limit ($400,000 total exposure), and the outstanding first mortgage balance sits at $200,000, the maximum allowable HELOC capacity equals $200,000 ($400,000 - $200,000).
Draw Period Interest-Only Equation vs. Repayment Recast
During the draw phase, borrowers typically remit interest accrued strictly against the active borrowed principal balance:
Interest accrues only on drawn capital, not the total credit limit. Principal repayment is voluntary, leaving the balance unchanged if minimum interest is paid.
Where P is outstanding principal at recast, i is monthly interest rate (APR / 12), and n is total repayment months (Repayment Years × 12).
The structural mathematical hazard of HELOCs is payment shock. At the exact month the draw window expires, the required remittance abruptly incorporates mandatory principal liquidation over the remaining compressed repayment schedule, frequently doubling or tripling the homeowner’s monthly cash outflow.
Equity Extraction Matrix: HELOC vs. HELOAN vs. Cash-Out Refi
Structural comparison of second liens, fixed home equity loans, and primary mortgage replacements
| Financial Mechanism | Interest Rate Structure | Disbursement Mode | Closing Cost Range | First Mortgage Status | Optimal Strategic Use Case |
|---|---|---|---|---|---|
| HELOC (Revolving Line) | Variable (Prime + Margin) | Revolving draw on-demand | $0 - $1,000 (Often waived) | Preserved intact at low rate | Staged home remodeling, standby emergency liquidity, seasonal business cash flow |
| Home Equity Loan (HELOAN) | Fixed (Established at close) | Lump-sum single funding | $1,500 - $3,500 | Preserved intact at low rate | Fixed-budget consolidation, major one-time roof/HVAC replacement, predictable budgeting |
| Cash-Out Refinance | Fixed or ARM (Market Rate) | Lump-sum net payout | 2% - 5% of entire mortgage | Extinguished & replaced entirely | Only advantageous if prevailing mortgage rates are lower than existing primary first lien |
*Critical Underwriting Rule: If your existing first mortgage carries a historically low rate (e.g., 2.75% to 3.5%), executing a cash-out refinance resets your entire principal balance to current elevated market rates. Utilizing a second lien HELOC leaves your underlying sub-4% primary loan undisturbed.
Frequently Asked Questions
Authoritative answers on home equity lines, draw period math, and recast payment risk
How does the draw period affect my HELOC payment calculations?
During the draw period (typically 5 to 10 years), the borrower is only obligated to make interest-only payments calculated on the active outstanding balance (Balance × Monthly Interest Rate). Once the line recasts into the repayment phase (usually 10 to 20 years), the borrower can no longer draw funds, and the balance is fully amortized into mandatory principal and interest payments.
How is maximum allowable HELOC borrowing capacity calculated using CLTV?
Lenders enforce a Combined Loan-to-Value (CLTV) ceiling, conventionally 80% to 85% of the appraised home value. Maximum line capacity equals (Appraised Home Value × Maximum CLTV) minus the First Mortgage Principal Balance. For instance, on a $500,000 home with an 80% CLTV limit and a $200,000 mortgage, the maximum line equals ($500,000 × 0.80) - $200,000 = $200,000.
What causes 'payment shock' when a HELOC transitions from draw to repayment?
Payment shock occurs at the end of the draw period because the required monthly payment abruptly shifts from small interest-only remittances to fully amortized principal-and-interest obligations over a compressed remaining term. If the outstanding balance was never reduced during the draw window, monthly payments can surge by 150% to 300% overnight.
Are HELOC interest payments tax-deductible under current IRS rules?
Under the Tax Cuts and Jobs Act (TCJA), HELOC interest is tax-deductible only if the borrowed proceeds are used to buy, build, or substantially improve the taxpayer's primary or secondary residence that secures the loan. Interest on HELOC funds used for debt consolidation, college tuition, or personal vehicles is non-deductible.
What is the difference between a variable-rate HELOC and a fixed-rate Home Equity Loan?
A HELOC is a revolving credit line carrying a variable interest rate indexed to the Wall Street Journal Prime Rate plus a lender margin, allowing borrowers to tap and repay funds repeatedly. A Home Equity Loan is a closed-end installment loan disbursed as a single lump sum with a fixed interest rate and equal monthly amortizing payments over 5 to 30 years.