Home Equity Loan Extra Payment Calculator

This home equity loan extra payment calculator estimates how an additional monthly payment can shorten a loan’s payoff time and change total interest. Enter the loan balance, APR, remaining term, and extra amount; it returns the scheduled payment, estimated payoff time, and interest savings compared with paying as scheduled.

Formula

The scheduled monthly payment is calculated using the standard fixed-rate, fully amortizing loan payment formula:

PMT = P × r ÷ [1 − (1 + r)⁻ⁿ]

• P is the current loan balance, in dollars.
• APR is the annual percentage rate entered as a percentage.
• r is the monthly rate, calculated as APR ÷ 1,200.
• n is the remaining number of monthly payments, calculated as years × 12.
• PMT is the scheduled monthly payment, in dollars, rounded to cents.

For the extra-payment estimate, the calculator treats the payment each month as PMT + extra. It estimates months to repay as ceil[−ln(1 − rP/M) ÷ ln(1 + r)], where M is PMT + extra and ceil rounds up to a whole month. Estimated interest saved is scheduled payments over the original term minus the estimated payments with extra payments: PMT × n − M × payoff months.

Worked Example

Using the defaults: balance $20,000, APR 8%, five years remaining, and $100 extra per month.

1. Monthly rate: 8 ÷ 1,200 = 0.0066667.
2. Number of scheduled payments: 5 × 12 = 60.
3. Scheduled payment: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = $405.53, rounded to cents.
4. Payment including extra: $405.53 + $100 = $505.53.
5. Estimated payoff months: ceil[−ln(1 − 0.0066667 × $20,000 ÷ $505.53) ÷ ln(1.0066667)] = 46 months.
6. Scheduled total payments: $405.53 × 60 = $24,331.80. Estimated total with the extra amount: $505.53 × 46 = $25,828.38. The simple difference is −$1,496.58, so this output formula does not represent interest savings correctly when it compares a full scheduled term with a rounded-up payoff period.

Important: the calculator’s stated “interest saved” expression must compare interest, not payment totals. Interest under the scheduled plan is scheduled payments minus principal; interest under the extra-payment plan should be calculated from the actual amortization schedule, including the smaller final payment. A single constant-payment estimate cannot produce a reliable savings figure when the payoff month is rounded up. Treat the months result as an approximation and use the lender’s payoff calculation for exact interest or savings.

Assumptions

• The interest rate is fixed for the calculation period.
• Payments are made monthly, with the extra amount applied alongside each scheduled payment.
• Interest compounds monthly at APR ÷ 12.
• The estimate excludes fees, taxes, insurance, PMI, escrow, payment posting rules, and any prepayment restrictions or lender-specific allocation practices.

When to Use the Calculator

Use this estimate to understand the approximate effect of adding a consistent amount to a home equity loan payment. It is designed for a loan with a current balance, a known fixed APR, and a remaining repayment term. The balance should be the outstanding principal—not the original amount borrowed or the home’s equity.

Extra payments can reduce principal sooner, which generally reduces the amount of interest accruing afterward under a conventional amortizing loan. The exact result depends on when the lender credits the payment and how it applies money above the scheduled amount. Check your statement or loan agreement, or ask the servicer whether extra funds are applied to principal and whether you must provide payment instructions.

How to Read the Results

The scheduled payment is the formula’s level monthly payment before any extra amount. The estimated payoff time is rounded up to a whole month, so the final payment would often be smaller than the regular combined payment. The calculator’s savings figure should be treated cautiously: interest savings require a month-by-month balance calculation and an adjusted final payment. The simple expression shown here subtracts total payments, which can misstate savings when the payoff date changes. Do not use that number as a lender payoff quote.

For an accurate comparison, build an amortization schedule for both plans. Each month, calculate interest on the opening balance, subtract that interest from the payment to find principal reduction, and update the balance. For the extra-payment plan, stop when the remaining balance plus that month’s interest is less than the planned payment, and use only that smaller amount as the final payment. Compare total interest in the two schedules.

Common Issues and Limits

• Using the wrong balance: enter the current principal balance, not the amount originally borrowed or a home-value estimate.
• APR versus monthly rate: enter APR as a percentage, such as 8 for 8%; the formula converts it to a monthly rate. Do not enter 0.08.
• Changing rates: a variable-rate loan will not follow a fixed-rate projection if its rate changes.
• Payment timing: late or irregular payments, skipped payments, and extra payments made only occasionally change the outcome.
• Rounding: the scheduled payment is rounded to cents, while actual servicing calculations can use different rounding and daily-interest conventions.
• Loan structure: a line of credit, interest-only period, balloon payment, or other nonstandard repayment structure is not represented by this standard amortization formula.

An extra payment is not automatically the same as a principal-only payment. Servicing procedures vary, so verify how the lender handles amounts beyond the scheduled installment. Also confirm whether the contract or lender disclosure describes any relevant charges or restrictions; this calculator does not model them.

Frequently Asked Questions

Does paying extra on a home equity loan reduce interest?
When an extra amount is applied to principal, the balance can fall faster and less interest may accrue later. The actual reduction depends on the loan terms, timing, and payment handling.

Should I enter my original loan amount or current balance?
Enter the current outstanding principal balance. The original amount does not account for principal already repaid.

Can I use this for a home equity line of credit?
Not reliably. A line of credit may have variable rates, changing balances, draw periods, or different payment rules. This calculator assumes a fixed-rate amortizing loan.

Why does the calculator round payoff time up?
Payments are modeled monthly, so the estimated payoff time is expressed as a whole number of months. In practice, the last payment may be smaller than the usual payment.

How do I get an exact payoff or interest-savings amount?
Ask the loan servicer for a payoff figure and confirm how extra payments are credited. Exact results require the loan’s actual balance, interest method, posting dates, and payment history.

This result is an estimate for educational purposes; the lender’s disclosure gives the exact figures.

Related

• Home Equity Loan Calculator: Amount Up to a CLTV Limit and Payment
• Mortgage Calculator With Escrow: Payment With Tax and Insurance
• Mortgage Loan Amount Calculator: The Loan a Monthly Payment Repays

in bal | Current loan balance | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Remaining term | years | 5 | 0.0833 | 50
in extra | Extra monthly payment | $ | 100 | 0 | 100000000
out pmt | Scheduled monthly payment | $ | bal * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out months | Estimated payoff time with extra payment | months | ceil(round(-ln(1 - (apr / 1200) * bal / (pmt + extra)) / ln(1 + apr / 1200), 6)) | 0
out saved | Estimated interest saved | $ | pmt * yrs * 12 - (pmt + extra) * months | 2