Calculate your estimated monthly mortgage payments.
Estimated Monthly Payment
$0.00
Understanding Your Mortgage Repayment Calculation
A mortgage is a significant financial commitment, and understanding how your monthly repayment is calculated is crucial for budgeting and financial planning. This calculator provides an estimate of your principal and interest payments, which form the core of your monthly mortgage cost. While it doesn't include property taxes, homeowner's insurance, or private mortgage insurance (PMI), it gives you a clear picture of the debt servicing part of your loan.
The Math Behind the Monthly Payment
The calculation is based on the standard annuity formula for loan payments. The formula determines a fixed periodic payment that will pay off the loan over its term with a specific interest rate.
The formula is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
M = Your total monthly mortgage payment (Principal & Interest)
P = The principal loan amount (the total 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 6%, your monthly rate (i) is 0.06 / 12 = 0.005.
n = The total number of payments over the loan's lifetime. This is calculated by multiplying the number of years in your loan term by 12. For example, a 30-year mortgage has 30 * 12 = 360 payments.
How to Use This Calculator
1. Loan Amount: Enter the total amount you intend to borrow for your home.
2. Annual Interest Rate: Input the yearly interest rate offered by your lender. This is often a key factor in determining your monthly payment.
3. Loan Term (Years): Specify how many years you plan to take to repay the loan. Longer terms generally mean lower monthly payments but more interest paid over time.
4. Calculate: Click the button to see your estimated monthly principal and interest payment.
5. Adjust: Use the sliders or input fields to experiment with different loan amounts, interest rates, and terms to see how they affect your payment. This can help you understand affordability and compare loan offers.
Important Considerations:
This calculator provides an estimate for the principal and interest (P&I) portion of your mortgage payment. Your actual total monthly housing expense will likely be higher because it typically includes:
Property Taxes: Paid to your local government.
Homeowner's Insurance: Required by lenders to protect against damage.
Private Mortgage Insurance (PMI): If your down payment is less than 20% of the home's value.
Homeowner Association (HOA) Fees: If applicable, for community amenities and maintenance.
Always consult with your mortgage lender for a precise loan estimate that includes all associated costs.
function calculateMortgage() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("interestRate").value);
var loanTermYears = parseInt(document.getElementById("loanTerm").value);
var monthlyPaymentElement = document.getElementById("monthlyPayment");
// Validate inputs
if (isNaN(loanAmount) || isNaN(annualInterestRate) || isNaN(loanTermYears) || loanAmount <= 0 || annualInterestRate < 0 || loanTermYears <= 0) {
monthlyPaymentElement.textContent = "Invalid input. Please enter valid numbers.";
return;
}
// Convert annual interest rate to monthly interest rate
var monthlyInterestRate = annualInterestRate / 100 / 12;
// Calculate the total number of payments
var numberOfPayments = loanTermYears * 12;
var monthlyPayment = 0;
// Handle the case of 0% interest rate
if (monthlyInterestRate === 0) {
monthlyPayment = loanAmount / numberOfPayments;
} else {
// Calculate monthly payment using the annuity formula
monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
}
// Format the result to two decimal places and add currency symbol
monthlyPaymentElement.textContent = "$" + monthlyPayment.toFixed(2);
}
function updateSlider(inputId, sliderId) {
var inputElement = document.getElementById(inputId);
var sliderElement = document.getElementById(sliderId);
var value = parseFloat(inputElement.value);
if (!isNaN(value)) {
sliderElement.value = value;
// Update slider track color based on its value
if (sliderElement.id === 'interestRateSlider') {
var rate = parseFloat(sliderElement.value);
var maxRate = parseFloat(sliderElement.max);
var percentage = (rate / maxRate) * 100;
sliderElement.style.background = 'linear-gradient(to right, #004a99 ' + percentage + '%, #e0e0e0 ' + percentage + '%)';
} else if (sliderElement.id === 'loanAmountSlider') {
var amount = parseFloat(sliderElement.value);
var maxAmount = parseFloat(sliderElement.max);
var percentage = (amount / maxAmount) * 100;
sliderElement.style.background = 'linear-gradient(to right, #004a99 ' + percentage + '%, #e0e0e0 ' + percentage + '%)';
} else if (sliderElement.id === 'loanTermSlider') {
var term = parseFloat(sliderElement.value);
var maxTerm = parseFloat(sliderElement.max);
var percentage = (term / maxTerm) * 100;
sliderElement.style.background = 'linear-gradient(to right, #004a99 ' + percentage + '%, #e0e0e0 ' + percentage + '%)';
}
}
}
function updateInput(sliderId, inputId) {
var sliderElement = document.getElementById(sliderId);
var inputElement = document.getElementById(inputId);
var value = parseFloat(sliderElement.value);
inputElement.value = value;
// Update slider track color based on its value
if (sliderElement.id === 'interestRateSlider') {
var rate = parseFloat(sliderElement.value);
var maxRate = parseFloat(sliderElement.max);
var percentage = (rate / maxRate) * 100;
sliderElement.style.background = 'linear-gradient(to right, #004a99 ' + percentage + '%, #e0e0e0 ' + percentage + '%)';
} else if (sliderElement.id === 'loanAmountSlider') {
var amount = parseFloat(sliderElement.value);
var maxAmount = parseFloat(sliderElement.max);
var percentage = (amount / maxAmount) * 100;
sliderElement.style.background = 'linear-gradient(to right, #004a99 ' + percentage + '%, #e0e0e0 ' + percentage + '%)';
} else if (sliderElement.id === 'loanTermSlider') {
var term = parseFloat(sliderElement.value);
var maxTerm = parseFloat(sliderElement.max);
var percentage = (term / maxTerm) * 100;
sliderElement.style.background = 'linear-gradient(to right, #004a99 ' + percentage + '%, #e0e0e0 ' + percentage + '%)';
}
}
// Initialize slider track colors on page load
document.addEventListener('DOMContentLoaded', function() {
updateSlider('loanAmount', 'loanAmountSlider');
updateSlider('interestRate', 'interestRateSlider');
updateSlider('loanTerm', 'loanTermSlider');
});