Home Equity Loan Calculator:
Fixed Rate P&I Formula, 10/15/20-Year Term Comparison, and HEL vs HELOC Total Interest Analysis

A home equity loan (HEL) — sometimes called a second mortgage — is a fixed-rate installment loan secured by the borrower’s home equity, junior in lien position to the first mortgage. Unlike a HELOC, which functions as a revolving credit line with a variable rate and interest-only draw period, a home equity loan delivers a single lump sum with a fixed monthly payment from the first statement. The payment never changes. The rate never changes. The balance declines predictably with each payment according to a fixed amortization schedule.

This predictability is the home equity loan’s defining advantage and its primary appeal relative to a HELOC: homeowners on fixed incomes, those managing tight budgets, and those who dislike the rate uncertainty of variable instruments all benefit from the home equity loan’s fixed-payment certainty. The tradeoff is that the full loan amount begins accruing interest from day one (versus a HELOC where you only pay interest on the amount actually drawn) and the payment cannot be reduced by repaying and redrawing as circumstances change. The home equity loan is the right product for borrowers who need a specific known amount, want rate certainty, and prefer mandatory principal paydown over the optional flexibility of a revolving line.

Home Equity Loan Formulas: Max Loan, Fixed Monthly Payment, and Term Tradeoffs

Home equity loan calculations use three formulas. The CLTV formula determines the maximum loan amount from available equity. The standard amortization formula determines the fixed monthly payment. The total interest formula reveals the full cost of the loan over its chosen term.

The third formula’s result — total interest — is the most important differentiator between home equity loans and HELOCs. The HEL’s mandatory principal paydown from month one means the outstanding balance declines steadily throughout the loan term, producing a progressively smaller interest component in each payment. The HELOC’s interest-only draw period (10 years with no principal reduction) means the full balance continues accruing interest for a decade before repayment amortization begins. On identical $100,000 balances at similar rates over comparable time horizons, the HEL consistently produces dramatically lower total interest than the HELOC — a gap that grows with the size of the balance and the duration of any HELOC draw period where minimum-only payments are made.

Four HEL Scenarios: Term Options, Total Interest, and Product Comparisons

The four cards below compare home equity loan economics across the critical decision dimensions: term selection (10, 15, 20 years), total interest comparison between HEL and HELOC on identical $100,000 amounts, and the HEL vs cash-out refinance decision based on existing mortgage rate context.

The second card’s comparison — $74,960 in total HEL interest versus $193,280 in total HELOC interest on identical $100,000 balances — deserves careful examination because the gap is larger than most borrowers expect. The HELOC’s 30-year total (10-year draw plus 20-year repayment) produces approximately 2.6 times more interest than the 15-year HEL. The source of this disparity: the HELOC’s 10-year interest-only draw period generates $101,040 in interest ($708/month x 120 months) while reducing the principal by exactly $0. The HEL in the same 15 years generates $74,960 in total interest while eliminating $100,000 in debt entirely. The HELOC’s lower monthly draw-period payment makes it feel cheaper, but the total interest math reveals the opposite over the full repayment horizon.

Complete HEL Calculation: $75,000 at 8.25% for 15 Years

The data block below traces the full home equity loan calculation for a $75,000 loan at 8.25% fixed for 15 years, showing the amortization formula steps, monthly payment, first-month principal/interest split, and total interest over the full term.

The data block’s first-month analysis reveals the HEL’s fundamental structure: in month one, $516 goes to interest and $211 reduces principal. By month 90 (year 7.5, midpoint), the balance has fallen to approximately $43,000, and the split is approximately $296 interest and $431 principal — more than double the month-one principal paydown. By month 170 (just 10 months from payoff), only $74 goes to interest and $653 accelerates the paydown. This progressive shift from interest-dominant to principal-dominant payments is the standard amortization schedule’s natural structure, and it means every extra principal payment made early in the HEL term has the highest possible interest-saving leverage.

HEL Term Comparison: Monthly Payment vs Total Interest by Amount and Term

The table below compares monthly payments and total interest costs across three loan amounts ($50,000, $100,000, $150,000) and three terms (10, 15, 20 years) at 8.25% fixed, enabling direct comparison of term tradeoffs at different borrowing levels.

The table’s most instructive column-pair comparison is 10-year versus 20-year on $100,000: monthly payment increases by $370 (43%) while total interest decreases by $58,440 (55%). The implicit “return” on the $370 extra monthly payment is approximately 8.25% per year — a guaranteed, risk-free (in the sense of certain interest savings) return equivalent to the HEL rate itself. In an environment where the HEL rate exceeds expected risk-free investment returns (such as Treasury yields), systematically choosing the shorter term and making the higher payment is financially superior to choosing the longer term and investing the difference. When expected investment returns significantly exceed the HEL rate, the longer term becomes the defensible choice — but for most borrowers using home equity loans for consumption purposes rather than investment, shorter terms reduce total cost.

HEL Amortization Milestones: Balance, Interest, and Principal Progression

The amortization table reveals that the crossover point — when principal exceeds interest in each monthly payment — occurs at approximately month 90 (year 7.5) on a 15-year HEL. Before this point, each payment is majority interest; after this point, each payment is majority principal. This crossover occurs earlier in shorter-term loans and later in longer-term loans. Borrowers who refinance or sell before the crossover point will have paid mostly interest with modest principal reduction — an argument for choosing the shortest affordable term to reach the equity-building crossover sooner.

Monthly HEL Payment by Amount and Term at 8.25%

The growth bars below show the monthly payment for five different HEL amounts at the 15-year term and 8.25% rate, providing a quick payment lookup before running the full calculation.

The growth bars confirm the linear scaling of home equity loan payments: each additional $25,000 in loan amount adds exactly $243/month to the fixed payment at 8.25% for 15 years ($972/month on $100,000 = 4 x $243/month on $25,000). This proportionality makes payment estimation straightforward: divide the desired loan amount by $25,000 and multiply by $243 for an approximate 15-year monthly payment at 8.25%. The total interest scales proportionally as well — $37,480 per $50,000, or approximately $0.75 of interest per $1.00 borrowed over the 15-year term at this rate.

HEL vs HELOC: The Comprehensive Total Interest Analysis

The comparison between home equity loans and HELOCs requires looking beyond the monthly payment to the total interest paid over the full repayment horizon. This analysis consistently shows that the HEL is significantly cheaper in total interest despite its higher monthly payment during the HELOC’s draw period.

HEL vs Cash-Out Refinance: The Rate Preservation Decision

For homeowners with first mortgage rates significantly below current market rates (common among those who purchased or refinanced in 2020-2022 when 30-year rates were 2.75-4.00%), the decision between a home equity loan and a cash-out refinance is one of the most financially consequential choices in residential real estate.

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Key Takeaways

The home equity loan provides fixed-rate, predictable-payment access to home equity through a lump-sum second mortgage with immediate principal paydown from month one. The standard amortization formula (M = P x r(1+r)^n / ((1+r)^n – 1)) determines the fixed monthly payment that will never change throughout the loan term. At 8.25% for 15 years, a $100,000 HEL costs $972/month and $74,960 in total interest — versus $193,280 in total interest for the same amount on a HELOC over its full 30-year life. This $118,320 difference, consistently hidden by the HELOC’s lower draw-period monthly payment, is the most important number in the home equity product comparison.

The three most consequential home equity loan decisions are: term selection (shorter terms save dramatically in total interest at the cost of higher monthly payments — the 10-year vs 20-year trade is $58,440 in savings for $370/month more), HEL versus HELOC (total interest analysis almost always favors the HEL for known single-amount borrowing needs), and HEL versus cash-out refinance (homeowners with below-market first mortgage rates should virtually always prefer a HEL over a cash-out refinance because preserving the below-market rate is worth substantially more than any first-mortgage-rate advantage a cash-out refi provides).