Mortgage Payment Calculator – Plan Your Home Loan
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Monthly Payment
$1,516.96
Total Principal
$240,000
Total Interest
$306,106
Total Cost of Loan
$546,106
Understanding Your Mortgage Calculation
Purchasing a home is likely the largest financial decision you will make in your lifetime. Our Mortgage Payment Calculator helps demystify the numbers, allowing you to estimate your monthly financial commitment based on current market rates and your personal savings for a down payment.
How the Formula Works
This calculator uses the standard amortization formula to determine your fixed monthly principal and interest payment:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
- M = Total monthly payment
- P = Principal loan amount (Home Price minus Down Payment)
- i = Monthly interest rate (Annual rate divided by 12)
- n = Number of payments (Loan term in years multiplied by 12)
Key Factors Affecting Your Mortgage
- Down Payment: A larger down payment reduces your principal loan amount. This not only lowers your monthly payment but can also save you tens of thousands of dollars in interest over the life of the loan. Generally, a down payment of 20% or more allows you to avoid Private Mortgage Insurance (PMI).
- Interest Rate: Even a fraction of a percentage point difference in your interest rate can dramatically impact the total cost of your home. Your rate is determined by the broader economy and your personal credit score.
- Loan Term: A 30-year term is standard, offering lower monthly payments but higher total interest costs. A 15-year term increases the monthly payment but allows you to build equity faster and pay significantly less interest.
What Isn't Included?
Keep in mind that this calculation covers Principal and Interest. To get a full picture of your housing costs ("PITI"), you should also budget for:
- Property Taxes: Usually calculated as a percentage of your home's assessed value.
- Homeowners Insurance: Required by lenders to protect the property against damage.
- HOA Fees: If buying in a managed community, these monthly fees cover common area maintenance.
function calculateMortgage() {
// 1. Get input values by ID
var homePriceInput = document.getElementById('homePrice');
var downPaymentInput = document.getElementById('downPayment');
var interestRateInput = document.getElementById('interestRate');
var loanTermInput = document.getElementById('loanTerm');
// 2. Parse values
var homePrice = parseFloat(homePriceInput.value);
var downPayment = parseFloat(downPaymentInput.value);
var annualRate = parseFloat(interestRateInput.value);
var years = parseFloat(loanTermInput.value);
// 3. Validation
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(annualRate) || isNaN(years)) {
alert("Please enter valid numbers in all fields.");
return;
}
if (downPayment >= homePrice) {
alert("Down payment cannot be greater than or equal to the home price.");
return;
}
// 4. Calculation Logic
var principal = homePrice – downPayment;
var monthlyRate = (annualRate / 100) / 12;
var numberOfPayments = years * 12;
var monthlyPayment = 0;
if (annualRate === 0) {
monthlyPayment = principal / numberOfPayments;
} else {
// Mortgage formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var x = Math.pow(1 + monthlyRate, numberOfPayments);
monthlyPayment = (principal * x * monthlyRate) / (x – 1);
}
var totalCost = monthlyPayment * numberOfPayments;
var totalInterest = totalCost – principal;
// 5. Update UI
// Helper function for currency formatting
var formatCurrency = function(num) {
return num.toLocaleString('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 0,
maximumFractionDigits: 0
});
};
document.getElementById('monthlyPayment').innerHTML = formatCurrency(monthlyPayment);
document.getElementById('totalPrincipal').innerHTML = formatCurrency(principal);
document.getElementById('totalInterest').innerHTML = formatCurrency(totalInterest);
document.getElementById('totalCost').innerHTML = formatCurrency(totalCost);
}