Enter your current loan details and a proposed extra monthly payment to see how much interest and time you could save.
Total Interest Saved
$0.00
Time Saved
0 Years, 0 Months
New Payoff Date
–
Required Monthly Payment (Base)
$0.00
Understanding the Power of Extra Mortgage Payments
A mortgage is likely the largest debt you will ever carry, but it is also one of the most flexible when it comes to long-term savings strategies. By utilizing a Mortgage Extra Payment Calculator, homeowners can visualize the massive impact of adding even a small amount to their principal payment every month.
How Mortgage Amortization Works
In the early years of a mortgage, the majority of your monthly payment goes toward interest, not the principal balance. This is due to amortization. The interest is calculated based on your remaining balance. Since the balance is highest at the start, the interest charge is highest.
When you make an extra principal-only payment, you directly reduce the balance upon which future interest is calculated. This creates a snowball effect: lower balance means less interest next month, which means more of your base payment goes to principal, further lowering the balance.
The Math Behind the Savings
Consider a $300,000 loan at 5% interest over 30 years. Your total interest paid over the life of the loan would be approximately $279,767. That is almost double the original loan amount!
However, by paying just $100 extra per month:
You reduce the term of the loan by several years.
You save tens of thousands of dollars in interest.
You build equity significantly faster.
Strategies for Paying Off Your Mortgage Early
Monthly Top-Up: Add a set amount (e.g., $50 or $100) to every bill.
Bi-Weekly Payments: Instead of paying monthly, pay half your payment every two weeks. This results in 26 half-payments, or 13 full payments per year.
Windfalls: Apply tax refunds, bonuses, or inheritances directly to the principal.
Is Prepaying Right for Everyone?
While saving on interest is attractive, it is important to weigh the opportunity cost. If your mortgage interest rate is very low (e.g., 3%), you might earn a higher return by investing that extra money in the stock market or a retirement account. However, for those seeking a guaranteed return and the peace of mind of being debt-free, extra mortgage payments are a powerful financial tool.
Disclaimer: This calculator provides estimates based on the inputs provided. Actual amortization schedules may vary slightly based on your lender's specific calculation methods and payment posting dates.
function calculateMortgageSavings() {
// 1. Get Input Values
var balance = parseFloat(document.getElementById('loanBalance').value);
var rate = parseFloat(document.getElementById('interestRate').value);
var years = parseFloat(document.getElementById('remainingYears').value);
var extra = parseFloat(document.getElementById('extraPayment').value);
// 2. Validation
if (isNaN(balance) || balance <= 0) {
alert("Please enter a valid loan balance.");
return;
}
if (isNaN(rate) || rate < 0) {
alert("Please enter a valid interest rate.");
return;
}
if (isNaN(years) || years <= 0) {
alert("Please enter valid remaining years.");
return;
}
if (isNaN(extra) || extra 0) {
// Apply interest for the month
var interestForMonth = currentBalance * monthlyRate;
// Determine principal portion
var principalForMonth = totalPaymentNew – interestForMonth;
// Handle last month case (if payment exceeds balance)
if (principalForMonth > currentBalance) {
principalForMonth = currentBalance;
// Recalculate interest strictly on remaining balance if needed,
// but usually simple interest applies to the remaining chunk.
}
totalInterestNew += interestForMonth;
currentBalance -= principalForMonth;
newMonths++;
// Safety break to prevent infinite loops in edge cases (e.g. interest > payment)
if (newMonths > 1200) break;
}
// 7. Calculate Savings
var interestSaved = totalInterestOriginal – totalInterestNew;
var monthsSaved = totalMonths – newMonths;
// Convert months saved to years and months
var yearsSaved = Math.floor(monthsSaved / 12);
var remainingMonthsSaved = 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();
// 8. Display Results
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
document.getElementById('interestSavedDisplay').innerText = formatter.format(interestSaved);
document.getElementById('timeSavedDisplay').innerText = yearsSaved + " Years, " + remainingMonthsSaved + " Months";
document.getElementById('newPayoffDateDisplay').innerText = payoffMonth + " " + payoffYear;
document.getElementById('basePaymentDisplay').innerText = formatter.format(basePayment) + "/mo";
document.getElementById('resultContainer').style.display = 'block';
}