Advanced Mortgage Payment Calculator
body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
margin: 0;
padding: 20px;
background-color: #f9f9f9;
}
.calculator-container {
max-width: 800px;
margin: 0 auto;
background: #fff;
padding: 30px;
border-radius: 12px;
box-shadow: 0 4px 20px rgba(0,0,0,0.1);
}
.calc-header {
text-align: center;
margin-bottom: 30px;
color: #2c3e50;
}
.input-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
.input-group {
margin-bottom: 15px;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #555;
}
.input-group input, .input-group select {
width: 100%;
padding: 12px;
border: 1px solid #ddd;
border-radius: 6px;
font-size: 16px;
box-sizing: border-box;
transition: border-color 0.3s;
}
.input-group input:focus {
border-color: #3498db;
outline: none;
}
.btn-container {
grid-column: 1 / -1;
text-align: center;
margin-top: 10px;
}
button.calc-btn {
background-color: #2ecc71;
color: white;
border: none;
padding: 15px 40px;
font-size: 18px;
font-weight: bold;
border-radius: 6px;
cursor: pointer;
transition: background-color 0.3s;
}
button.calc-btn:hover {
background-color: #27ae60;
}
#results-area {
margin-top: 30px;
background-color: #f1f8ff;
padding: 25px;
border-radius: 8px;
display: none;
border: 1px solid #d1e3f8;
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.result-row {
display: flex;
justify-content: space-between;
padding: 10px 0;
border-bottom: 1px solid #e1e4e8;
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.result-row:last-child {
border-bottom: none;
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.result-label {
color: #666;
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.result-value {
font-weight: bold;
color: #2c3e50;
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.total-payment {
font-size: 24px;
color: #2980b9;
margin-top: 10px;
padding-top: 10px;
border-top: 2px solid #bdc3c7;
}
.content-section {
max-width: 800px;
margin: 40px auto;
background: #fff;
padding: 30px;
border-radius: 12px;
box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}
h2 {
color: #2c3e50;
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padding-bottom: 10px;
margin-top: 30px;
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p {
margin-bottom: 15px;
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ul {
margin-bottom: 15px;
padding-left: 20px;
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li {
margin-bottom: 8px;
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@media (max-width: 600px) {
.input-grid {
grid-template-columns: 1fr;
}
}
Monthly Payment Breakdown
Principal & Interest:
$0.00
Property Tax:
$0.00
Home Insurance:
$0.00
Total Monthly Payment:
$0.00
*Loan Amount: $0
Understanding Your Mortgage Calculation
Buying a home is often the largest financial decision a person will make in their lifetime. Using our Mortgage Payment Calculator helps you estimate your monthly housing costs accurately by factoring in not just the loan repayment, but also necessary ongoing expenses like property taxes and homeowners insurance.
Knowing your "all-in" monthly cost is crucial for budgeting and ensuring you don't become "house poor"—a situation where too much of your income goes toward housing expenses, leaving little for savings or other lifestyle needs.
How the Formula Works
This calculator uses the standard amortization formula to determine your monthly Principal and Interest (P&I) payment:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
- M = Total monthly payment (P&I)
- P = Principal loan amount (Home Price minus Down Payment)
- i = Monthly interest rate (Annual Rate / 12)
- n = Number of payments (Loan Term in years × 12)
Additionally, we take your annual property tax and home insurance inputs and divide them by 12 to give you a realistic view of the money that will leave your bank account every month.
Factors Affecting Your Mortgage Payment
Several variables can significantly impact how much you pay:
- Down Payment: A larger down payment reduces the principal loan amount, which lowers your monthly payment and the total interest paid over the life of the loan.
- Interest Rate: Even a small difference in rates (e.g., 0.5%) can change your monthly payment by hundreds of dollars. Your credit score largely determines the rate you qualify for.
- Loan Term: A 30-year term offers lower monthly payments but results in higher total interest costs compared to a 15-year term.
- Taxes & Insurance: These are often held in escrow by your lender. Property taxes vary widely by location, while insurance depends on the home's value and coverage level.
Frequently Asked Questions
What is Principal vs. Interest?
Principal is the money that goes toward paying off the loan balance itself. Interest is the cost of borrowing that money. In the early years of a mortgage, the majority of your payment goes toward interest. As the loan matures, a larger portion shifts toward paying down the principal.
Does this calculator include PMI?
This specific calculator focuses on P&I, taxes, and insurance. If your down payment is less than 20% of the home price, lenders typically require Private Mortgage Insurance (PMI), which would be an additional cost on top of the estimate provided here. A typical PMI rate ranges from 0.5% to 1% of the loan amount annually.
How much of my income should go to a mortgage?
A common rule of thumb is the 28/36 rule. Your mortgage payment (including taxes and insurance) should not exceed 28% of your gross monthly income, and your total debt payments (mortgage + cars + credit cards) should not exceed 36%.
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');
var taxInput = document.getElementById('propertyTax');
var insuranceInput = document.getElementById('insurance');
// 2. Parse values to floats
var price = parseFloat(homePriceInput.value);
var down = parseFloat(downPaymentInput.value);
var annualRate = parseFloat(interestRateInput.value);
var years = parseFloat(loanTermInput.value);
var annualTax = parseFloat(taxInput.value);
var annualInsurance = parseFloat(insuranceInput.value);
// 3. Validation Logic
if (isNaN(price) || price <= 0) {
alert("Please enter a valid Home Price.");
return;
}
if (isNaN(down) || down < 0) {
down = 0; // Default to 0 if invalid but var it proceed
}
if (isNaN(annualRate) || annualRate < 0) {
alert("Please enter a valid Interest Rate.");
return;
}
if (isNaN(years) || years <= 0) {
alert("Please check the Loan Term.");
return;
}
// 4. Calculate Loan Variables
var principal = price – down;
if (principal <= 0) {
alert("Down payment cannot be greater than or equal to Home Price.");
return;
}
var monthlyRate = (annualRate / 100) / 12;
var numberOfPayments = years * 12;
// 5. Calculate Monthly P&I
// Formula: M = P[r(1+r)^n/((1+r)^n)-1)]
var monthlyPI = 0;
if (annualRate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
var x = Math.pow(1 + monthlyRate, numberOfPayments);
monthlyPI = (principal * x * monthlyRate) / (x – 1);
}
// 6. Calculate Taxes and Insurance Monthly
var monthlyTax = isNaN(annualTax) ? 0 : annualTax / 12;
var monthlyInsurance = isNaN(annualInsurance) ? 0 : annualInsurance / 12;
// 7. Total Monthly Payment
var totalMonthly = monthlyPI + monthlyTax + monthlyInsurance;
// 8. Format Currency Helper
function formatMoney(num) {
return "$" + num.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
// 9. Update DOM
document.getElementById('res-principal-interest').innerText = formatMoney(monthlyPI);
document.getElementById('res-tax').innerText = formatMoney(monthlyTax);
document.getElementById('res-insurance').innerText = formatMoney(monthlyInsurance);
document.getElementById('res-total').innerText = formatMoney(totalMonthly);
document.getElementById('res-loan-amount').innerText = formatMoney(principal);
// Show results area
document.getElementById('results-area').style.display = 'block';
}