Mortgage Calculator – Plan Your Home Loan
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Mortgage Payment Calculator
Estimate your monthly mortgage payments accurately by entering your home price, down payment, interest rate, and loan term.
Monthly Payment:
$0.00
Total Principal:
$0.00
Total Interest:
$0.00
Total Cost of Loan:
$0.00
Understanding Your Mortgage Calculation
Purchasing a home is likely the largest financial decision you will make in your lifetime. Understanding how your monthly mortgage payment is calculated is crucial for maintaining financial health. This calculator uses the standard amortization formula to determine your principal and interest payments.
How the Mortgage Formula Works
The standard formula used by lenders to calculate your monthly payment (M) is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
- P (Principal): This is the loan amount (Home Price minus Down Payment).
- i (Monthly Interest Rate): Your annual interest rate divided by 12.
- n (Number of Payments): The total number of months in your loan term (Years × 12).
Factors Affecting Your Monthly Payment
Several variables impact how much you will pay each month:
- Down Payment: A larger down payment reduces your principal loan amount, which lowers your monthly payment and the total interest paid over the life of the loan. Putting down at least 20% also helps you avoid Private Mortgage Insurance (PMI).
- Interest Rate: Even a fraction of a percentage point can significantly alter your monthly payment. Interest rates are determined by broader economic factors 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 has higher monthly payments but saves a substantial amount in interest over time.
Example Calculation
Let's say you buy a home for $300,000 with a $60,000 (20%) down payment. Your loan amount is $240,000. If you secure a 30-year fixed-rate loan at 6.5%:
- Your estimated monthly principal and interest payment would be roughly $1,517.
- Over the life of the loan, you would pay approximately $306,000 in interest alone.
Use the calculator above to run your own scenarios and find a budget that works for you.
function calculateMortgage() {
// 1. Get Input Values by ID
var priceInput = document.getElementById("homePrice");
var downInput = document.getElementById("downPayment");
var rateInput = document.getElementById("interestRate");
var termInput = document.getElementById("loanTerm");
var errorDisplay = document.getElementById("errorDisplay");
// 2. Parse Values
var price = parseFloat(priceInput.value);
var down = parseFloat(downInput.value);
var rate = parseFloat(rateInput.value);
var years = parseFloat(termInput.value);
// 3. Validation
if (isNaN(price) || isNaN(down) || isNaN(rate) || isNaN(years) || price <= 0 || years <= 0) {
errorDisplay.style.display = "block";
return;
} else {
errorDisplay.style.display = "none";
}
// 4. Logic Implementation
var principal = price – down;
// Handle case where down payment is greater than price
if (principal < 0) {
principal = 0;
}
var monthlyInterest = rate / 100 / 12;
var numberOfPayments = years * 12;
var monthlyPayment = 0;
var totalCost = 0;
var totalInterest = 0;
// If interest rate is 0, simple division
if (rate === 0) {
monthlyPayment = principal / numberOfPayments;
} else {
// Standard Amortization Formula
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var x = Math.pow(1 + monthlyInterest, numberOfPayments);
monthlyPayment = (principal * monthlyInterest * x) / (x – 1);
}
// Calculate Totals
totalCost = monthlyPayment * numberOfPayments;
totalInterest = totalCost – principal;
// 5. Update UI
// Helper function for currency formatting
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
document.getElementById("monthlyPaymentResult").innerHTML = formatter.format(monthlyPayment);
document.getElementById("principalResult").innerHTML = formatter.format(principal);
document.getElementById("totalInterestResult").innerHTML = formatter.format(totalInterest);
document.getElementById("totalCostResult").innerHTML = formatter.format(totalCost);
}