Mortgage Amortization Calculator with Extra Payments
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Mortgage Amortization Calculator with Extra Payments
Results
Total Paid: $0 |
Total Interest Paid: $0 |
Loan Paid Off In: 0 months
Amortization Schedule
| Month |
Starting Balance |
Payment |
Principal |
Interest |
Ending Balance |
Understanding Your Mortgage Amortization with Extra Payments
A mortgage is a significant financial commitment, and understanding how your loan is repaid over time is crucial. An amortization schedule is a table that breaks down each monthly mortgage payment into its principal and interest components. For most fixed-rate mortgages, the total monthly payment remains constant, but the proportion allocated to principal and interest changes over the life of the loan. Initially, a larger portion goes towards interest, and as you pay down the principal, more of your payment goes towards reducing the loan amount.
Why Make Extra Payments?
Adding extra money to your monthly mortgage payment, even a small amount, can have a substantial impact on the total interest paid and the loan's payoff time. By consistently paying more than the scheduled amount, you directly reduce the principal balance faster. This means less interest accrues over time because interest is calculated on the remaining principal.
How the Calculator Works:
This calculator takes your initial loan details—principal amount, annual interest rate, and loan term in years—and calculates your standard monthly payment using the following formula:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
M = Your total monthly mortgage payment (principal and interest)P = The principal loan amounti = Your monthly interest rate (annual rate divided by 12)n = The total number of payments over the loan's lifetime (loan term in years multiplied by 12)
Then, it incorporates any extra monthly payments you specify. For each month:
- The standard monthly payment (principal + interest) is calculated.
- The extra payment amount is added to the principal portion.
- The interest for that month is calculated based on the starting balance.
- The principal paid is the total payment (standard + extra) minus the interest.
- The ending balance is the starting balance minus the principal paid.
The calculator continues this process month by month, updating the balance and recalculating interest until the loan balance reaches zero. It tracks the total amount paid, the total interest accumulated, and the total number of months it takes to pay off the loan, including the impact of your extra payments.
Benefits of Using Extra Payments:
- Save Money on Interest: The most significant benefit is reducing the overall interest paid over the life of the loan.
- Pay Off Your Mortgage Faster: Shorten the loan term and achieve homeownership freedom sooner.
- Build Equity Quicker: Your investment in your home grows more rapidly as you pay down the principal.
- Financial Flexibility: Paying off your mortgage early can free up significant cash flow in retirement or for other financial goals.
Important Considerations:
- Verify with Your Lender: Always confirm with your mortgage lender how extra payments are applied. Some lenders may require you to specify that extra payments should go towards the principal.
- No Prepayment Penalties: Ensure your mortgage doesn't have any prepayment penalties, although these are rare for most residential mortgages in many regions.
- Consistency is Key: Even small, consistent extra payments can lead to substantial savings over time.
Use this calculator to explore different extra payment scenarios and see the powerful impact it can have on your mortgage payoff journey.
function calculateMortgage() {
var principal = parseFloat(document.getElementById("loanAmount").value);
var annualRate = parseFloat(document.getElementById("annualInterestRate").value);
var years = parseInt(document.getElementById("loanTermYears").value);
var extraPayment = parseFloat(document.getElementById("extraPaymentAmount").value);
// — Input Validation —
if (isNaN(principal) || principal <= 0) {
alert("Please enter a valid Loan Amount.");
return;
}
if (isNaN(annualRate) || annualRate < 0) {
alert("Please enter a valid Annual Interest Rate.");
return;
}
if (isNaN(years) || years <= 0) {
alert("Please enter a valid Loan Term in Years.");
return;
}
if (isNaN(extraPayment) || extraPayment 0) {
standardMonthlyPayment = principal * (monthlyRate * Math.pow(1 + monthlyRate, numberOfMonths)) / (Math.pow(1 + monthlyRate, numberOfMonths) – 1);
} else {
standardMonthlyPayment = principal / numberOfMonths; // Handle 0% interest rate
}
// — Amortization Calculation —
var balance = principal;
var totalPaid = 0;
var totalInterestPaid = 0;
var monthCounter = 0;
var amortizationData = [];
// Ensure extra payment doesn't exceed total required payment if principal is very low
var effectiveExtraPayment = extraPayment;
while (balance > 0.005) { // Use a small threshold to account for floating point inaccuracies
monthCounter++;
var interestPayment = balance * monthlyRate;
var principalPayment;
var totalPaymentForMonth = standardMonthlyPayment + effectiveExtraPayment;
// Adjust payment if it would overpay the loan in the final month
if (totalPaymentForMonth > balance + interestPayment) {
totalPaymentForMonth = balance + interestPayment;
principalPayment = balance;
interestPayment = totalPaymentForMonth – principalPayment; // Recalculate interest based on final principal
} else {
principalPayment = totalPaymentForMonth – interestPayment;
}
// Ensure principal payment doesn't exceed remaining balance due to floating point errors
if (principalPayment > balance) {
principalPayment = balance;
totalPaymentForMonth = principalPayment + interestPayment;
}
balance -= principalPayment;
totalPaid += totalPaymentForMonth;
totalInterestPaid += interestPayment;
// Cap balance at 0 to prevent negative values due to rounding
if (balance < 0) {
balance = 0;
}
amortizationData.push({
month: monthCounter,
startingBalance: parseFloat(arguments[0][monthCounter-1] ? arguments[0][monthCounter-1].endingBalance : principal), // previous month's ending balance
payment: totalPaymentForMonth,
principal: principalPayment,
interest: interestPayment,
endingBalance: balance
});
}
// — Display Results —
document.getElementById("result-section").style.display = "block";
document.getElementById("totalPaid").textContent = "$" + totalPaid.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
document.getElementById("totalInterestPaid").textContent = "$" + totalInterestPaid.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
document.getElementById("loanPaidOffIn").textContent = monthCounter + " months";
// — Populate Amortization Table —
var tableBody = document.getElementById("amortization-table").getElementsByTagName("tbody")[0];
tableBody.innerHTML = ""; // Clear previous data
var currentBalance = principal;
for (var i = 0; i < amortizationData.length; i++) {
var row = tableBody.insertRow();
var monthData = amortizationData[i];
var cellMonth = row.insertCell(0);
var cellStartBalance = row.insertCell(1);
var cellPayment = row.insertCell(2);
var cellPrincipal = row.insertCell(3);
var cellInterest = row.insertCell(4);
var cellEndBalance = row.insertCell(5);
cellMonth.textContent = monthData.month;
cellStartBalance.textContent = "$" + currentBalance.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
cellPayment.textContent = "$" + monthData.payment.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
cellPrincipal.textContent = "$" + monthData.principal.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
cellInterest.textContent = "$" + monthData.interest.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
cellEndBalance.textContent = "$" + monthData.endingBalance.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
currentBalance = monthData.endingBalance; // Update for next iteration's starting balance display
}
}