Estimate your monthly payments and interest costs.
30 Years
20 Years
15 Years
10 Years
Please enter valid positive numbers for all fields.
Estimated Monthly Payment$0.00
Principal & Interest:$0.00
Property Taxes (Monthly):$0.00
Home Insurance (Monthly):$0.00
HOA Fees:$0.00
Total Loan Amount:$0.00
Total Interest Paid:$0.00
Total Cost of Loan:$0.00
function calculateMortgage() {
// 1. Get Input Values
var homePrice = parseFloat(document.getElementById("mc_homePrice").value);
var downPayment = parseFloat(document.getElementById("mc_downPayment").value);
var interestRate = parseFloat(document.getElementById("mc_interestRate").value);
var loanTermYears = parseInt(document.getElementById("mc_loanTerm").value);
var annualTax = parseFloat(document.getElementById("mc_propertyTax").value);
var annualIns = parseFloat(document.getElementById("mc_insurance").value);
var monthlyHOA = parseFloat(document.getElementById("mc_hoa").value);
// 2. Validation
var errorDiv = document.getElementById("mc_error");
var resultDiv = document.getElementById("mc_resultSection");
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) ||
isNaN(annualTax) || isNaN(annualIns) || isNaN(monthlyHOA) ||
homePrice < 0 || downPayment < 0 || interestRate < 0) {
errorDiv.style.display = "block";
resultDiv.style.display = "none";
return;
}
errorDiv.style.display = "none";
// 3. Core Calculations
var principal = homePrice – downPayment;
// Handle case where down payment is greater than home price
if (principal < 0) principal = 0;
var monthlyRate = (interestRate / 100) / 12;
var numberOfPayments = loanTermYears * 12;
var monthlyPrincipalAndInterest = 0;
// If interest rate is 0, just divide principal by months
if (interestRate === 0) {
monthlyPrincipalAndInterest = principal / numberOfPayments;
} else {
// Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var x = Math.pow(1 + monthlyRate, numberOfPayments);
monthlyPrincipalAndInterest = (principal * x * monthlyRate) / (x – 1);
}
// Monthly Escrow components
var monthlyTax = annualTax / 12;
var monthlyIns = annualIns / 12;
// Total Monthly
var totalMonthlyPayment = monthlyPrincipalAndInterest + monthlyTax + monthlyIns + monthlyHOA;
// Totals over life of loan
var totalPaymentOverLife = (monthlyPrincipalAndInterest * numberOfPayments);
var totalInterestPaid = totalPaymentOverLife – principal;
var totalCostWithEscrow = (totalMonthlyPayment * numberOfPayments);
// 4. Formatting Helper
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
// 5. Output Results
document.getElementById("mc_totalMonthlyPayment").innerHTML = formatter.format(totalMonthlyPayment);
document.getElementById("mc_pi").innerHTML = formatter.format(monthlyPrincipalAndInterest);
document.getElementById("mc_tax").innerHTML = formatter.format(monthlyTax);
document.getElementById("mc_ins").innerHTML = formatter.format(monthlyIns);
document.getElementById("mc_hoa_res").innerHTML = formatter.format(monthlyHOA);
document.getElementById("mc_loanAmount").innerHTML = formatter.format(principal);
document.getElementById("mc_totalInterest").innerHTML = formatter.format(totalInterestPaid);
document.getElementById("mc_totalCost").innerHTML = formatter.format(totalCostWithEscrow);
// Show result section
resultDiv.style.display = "block";
}
Comprehensive Mortgage Repayment Guide
Buying a home is one of the most significant financial decisions you will make. Understanding your monthly mortgage obligation is crucial for maintaining financial health. This Mortgage Repayment Calculator is designed to give you a detailed breakdown of your expected costs, going beyond simple principal and interest to include taxes, insurance, and HOA fees.
How Is Your Monthly Mortgage Payment Calculated?
Your monthly payment is typically composed of four main parts, often referred to as PITI (Principal, Interest, Taxes, and Insurance):
Principal: The portion of the payment that reduces the remaining balance of the loan. In the early years of a mortgage, this amount is small, but it grows over time.
Interest: The cost of borrowing money. This usually makes up the bulk of your payment in the first few years of the loan term.
Taxes: Property taxes assessed by your local government. Lenders often collect this monthly and hold it in an escrow account to pay the bill annually.
Insurance: Homeowners insurance protects against damage. Like taxes, this is often paid through an escrow account.
Understanding the Formula
The core of the mortgage calculation relies on a standard amortization formula:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
Where:
M = Total monthly payment
P = Principal loan amount (Home Price minus Down Payment)
i = Monthly interest rate (Annual rate divided by 12)
n = Total number of months (Loan term in years multiplied by 12)
Why Your Down Payment Matters
The size of your down payment significantly impacts your monthly costs and the total interest paid over the life of the loan. A larger down payment reduces the principal loan amount (P), which lowers both your monthly payment and the total interest accrued.
Furthermore, if your down payment is less than 20% of the home price, lenders typically require Private Mortgage Insurance (PMI). While our calculator includes HOA fees and standard insurance, remember to factor in potential PMI costs if you are putting down less than 20%.
15-Year vs. 30-Year Fixed Mortgages
One of the most common questions homebuyers have is whether to choose a 15-year or 30-year term.
Feature
30-Year Mortgage
15-Year Mortgage
Monthly Payment
Lower
Higher
Interest Rate
Typically Higher
Typically Lower
Total Interest Paid
High
Significantly Lower
Building Equity
Slower
Faster
Strategies to Lower Your Payment
If the estimated payment from the calculator is higher than your budget allows, consider these strategies:
Boost your credit score: A higher score can qualify you for a lower interest rate.
Shop for insurance: Homeowners insurance rates vary; shopping around can save you hundreds per year.
Increase your down payment: Saving longer to put more down reduces the loan size.
Consider points: You can pay "points" upfront to lower the interest rate on the loan.
Using This Calculator for Refinancing
This tool is also excellent for analyzing potential refinance options. Simply enter the outstanding balance of your current mortgage as the "Home Price" (and set Down Payment to 0), or enter your home's current value and your equity as the down payment. Compare the result with your current bill to see if refinancing makes financial sense.