Mortgage Extra Payment Calculator – Calculate Interest Savings
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Mortgage Extra Payment Calculator
Your Savings Analysis
Total Interest Saved:
$0.00
Time Saved:
0 Years, 0 Months
New Payoff Date:
–
Original Total Interest:
$0.00
New Total Interest:
$0.00
*Calculations assume fixed interest rate and consistent payments.
function calculateMortgageSavings() {
// Get Input Values
var balance = parseFloat(document.getElementById('loanBalance').value);
var rate = parseFloat(document.getElementById('interestRate').value);
var years = parseFloat(document.getElementById('remainingTerm').value);
var extra = parseFloat(document.getElementById('extraPayment').value);
// Validation
if (isNaN(balance) || isNaN(rate) || isNaN(years)) {
alert("Please enter valid numbers for Balance, Rate, and Term.");
return;
}
if (isNaN(extra)) {
extra = 0;
}
if (balance <= 0 || rate < 0 || years <= 0 || extra 0) {
// Safety break for infinite loops
if (newMonths > 1000) break;
var interestForMonth = currentBalance * monthlyRate;
var principalForMonth = totalPaymentNew – interestForMonth;
// Handle last month case
if (currentBalance < principalForMonth) {
interestForMonth = currentBalance * monthlyRate; // Interest on remaining
principalForMonth = currentBalance; // Pay off rest
}
totalInterestNew += interestForMonth;
currentBalance -= principalForMonth;
newMonths++;
}
// Calculate Savings
var interestSaved = totalInterestOriginal – totalInterestNew;
var monthsSaved = totalMonthsOriginal – newMonths;
var yearsSaved = Math.floor(monthsSaved / 12);
var remainingMonthsSaved = Math.round(monthsSaved % 12);
// Calculate New Payoff Date
var today = new Date();
today.setMonth(today.getMonth() + newMonths);
var payoffMonth = today.toLocaleString('default', { month: 'long' });
var payoffYear = today.getFullYear();
// Update UI
document.getElementById('resultsArea').style.display = 'block';
document.getElementById('totalInterestSaved').innerText = "$" + interestSaved.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('timeSaved').innerText = yearsSaved + " Years, " + remainingMonthsSaved + " Months";
document.getElementById('newPayoffDate').innerText = payoffMonth + " " + payoffYear;
document.getElementById('originalInterest').innerText = "$" + totalInterestOriginal.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('newInterest').innerText = "$" + totalInterestNew.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
}
How Extra Mortgage Payments Save You Money
Making extra payments on your mortgage principal is one of the most effective guaranteed returns on investment available to homeowners. Because mortgages are amortized, the majority of your payments in the early years go toward interest rather than the principal balance. By making extra payments, you directly reduce the principal, which in turn reduces the interest charged in every subsequent month for the life of the loan.
Understanding Amortization and Principal Reduction
Every time you make a mortgage payment, the bank calculates the interest due based on your current outstanding balance. If your balance is $300,000 at 6%, your monthly interest charge is $1,500. If you pay an extra $5,000 one month, your balance drops to $295,000. Next month, the interest is calculated on $295,000, reducing the charge to roughly $1,475.
That $25 saving happens every single month for the remainder of the loan term. This "snowball effect" is why even small extra payments can shave years off your mortgage term.
Strategies for Paying Off Your Mortgage Faster
There are several ways to utilize this calculator to plan your debt-free journey:
- The "Round Up" Method: If your mortgage payment is $1,840, round it up to $2,000. That extra $160 goes straight to principal.
- Bi-Weekly Payments: Instead of paying monthly, pay half your mortgage payment every two weeks. Since there are 52 weeks in a year, you end up making 26 half-payments, which equals 13 full payments per year—one extra payment annually without feeling the pinch.
- Windfalls: Apply tax refunds, work bonuses, or inheritance money directly to the principal balance using the "Current Loan Balance" field above to see the impact.
Why Use This Mortgage Extra Payment Calculator?
This tool is designed to provide transparency that standard amortization schedules hide. By inputting your specific loan details—including Current Loan Balance, Interest Rate, and Remaining Term—you can visualize exactly how powerful your extra cash flow can be.
For example, on a $250,000 loan with 25 years remaining at 6.5%, paying just an extra $200 per month could save you over $60,000 in interest and pay off the loan 5 years early. Use the tool above to run your own numbers.