A fixed-rate mortgage is a home loan where the interest rate remains the same for the entire duration of the loan. This provides predictability, as your monthly principal and interest payment will not change, making budgeting easier. This calculator helps you estimate your monthly payments, total interest paid, and the total amount repaid over the life of the loan.
How the Calculation Works
The standard formula for calculating a fixed monthly mortgage payment (M) is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
M = Your total monthly mortgage payment (principal and interest)
P = The principal loan amount (the amount you borrow)
i = Your *monthly* interest rate. This is calculated by dividing your Annual Interest Rate by 12. For example, if your annual rate is 5.5%, your monthly rate is 0.055 / 12 = 0.0045833.
n = The total number of payments over the loan's lifetime. This is calculated by multiplying your Loan Term in Years by 12. For example, a 30-year mortgage has 30 * 12 = 360 payments.
Example Calculation
Let's assume you are taking out a mortgage with the following details:
This means your estimated monthly payment for principal and interest would be approximately $1,736.75.
Additional Calculations
Once the monthly payment (M) is calculated:
Total Amount Paid:M * n (e.g., $1,736.75 * 360 = $625,230)
Total Interest Paid:(M * n) - P (e.g., $625,230 - $300,000 = $325,230)
Note: This calculator provides an estimate and does not include other costs associated with homeownership, such as property taxes, homeowner's insurance, or potential Private Mortgage Insurance (PMI). These additional costs are often included in an actual mortgage payment and are known as PITI (Principal, Interest, Taxes, and Insurance).
var loanAmountInput = document.getElementById('loanAmount');
var annualInterestRateInput = document.getElementById('annualInterestRate');
var loanTermInput = document.getElementById('loanTerm');
var loanTermValueSpan = document.getElementById('loanTermValue');
var monthlyPaymentResultSpan = document.getElementById('monthlyPaymentResult');
var totalInterestResultSpan = document.getElementById('totalInterestResult');
var totalPaymentResultSpan = document.getElementById('totalPaymentResult');
// Update displayed loan term value as slider changes
loanTermInput.oninput = function() {
loanTermValueSpan.textContent = this.value + ' years';
};
function calculateMortgage() {
var loanAmount = parseFloat(loanAmountInput.value);
var annualInterestRate = parseFloat(annualInterestRateInput.value);
var loanTermYears = parseInt(loanTermInput.value);
// Basic validation
if (isNaN(loanAmount) || loanAmount <= 0) {
alert("Please enter a valid loan amount.");
return;
}
if (isNaN(annualInterestRate) || annualInterestRate 100) {
alert("Please enter a valid annual interest rate between 0% and 100%.");
return;
}
if (isNaN(loanTermYears) || loanTermYears <= 0) {
alert("Please select a valid loan term.");
return;
}
var monthlyInterestRate = annualInterestRate / 100 / 12;
var numberOfPayments = loanTermYears * 12;
var monthlyPayment = 0;
// Handle case for 0% interest rate
if (monthlyInterestRate === 0) {
monthlyPayment = loanAmount / numberOfPayments;
} else {
monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
}
var totalPayment = monthlyPayment * numberOfPayments;
var totalInterest = totalPayment – loanAmount;
// Format results to two decimal places and add currency symbol
monthlyPaymentResultSpan.textContent = "$" + monthlyPayment.toFixed(2);
totalInterestResultSpan.textContent = "$" + totalInterest.toFixed(2);
totalPaymentResultSpan.textContent = "$" + totalPayment.toFixed(2);
}
// Initial calculation on page load with default values
window.onload = function() {
loanTermValueSpan.textContent = loanTermInput.value + ' years';
calculateMortgage();
};