Based on your inputs, your principal and interest payment is estimated to be:
Loan Amount:$0.00
Interest Rate:0.00%
Loan Term:0 Years
Understanding Your Mortgage Payment
A mortgage is a significant financial commitment, and understanding how your monthly payment is calculated is crucial. This calculator helps you estimate the principal and interest portion of your monthly mortgage payment, allowing you to budget effectively.
The Mortgage Payment Formula
The standard formula used to calculate the monthly payment (M) for a fixed-rate mortgage is as follows:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
M = Your total monthly mortgage payment (principal and interest)
P = The principal loan amount (the amount you borrow)
i = Your monthly interest rate. This is calculated by dividing your annual interest rate by 12. For example, a 5% annual rate becomes 0.05 / 12.
n = The total number of payments over the loan's lifetime. This is calculated by multiplying the loan term in years by 12. For a 30-year mortgage, n = 30 * 12 = 360.
How the Calculator Works
This calculator takes the following inputs from you:
Loan Amount (P): The total sum of money you are borrowing to purchase your home.
Annual Interest Rate (%): The yearly rate of interest charged by the lender. The calculator converts this to a monthly rate (i) by dividing by 12.
Loan Term (Years): The duration of the loan, typically 15, 20, or 30 years. The calculator converts this to the total number of monthly payments (n) by multiplying by 12.
It then applies the formula above to compute your estimated monthly principal and interest payment.
Important Considerations
What's Not Included: This calculator *only* estimates the principal and interest (P&I) payment. Your actual total monthly housing expense will likely be higher and include:
Property Taxes: Taxes levied by your local government.
Homeowners Insurance: Insurance protecting your home against damage.
Private Mortgage Insurance (PMI): If your down payment is less than 20%, lenders often require PMI.
Homeowners Association (HOA) Fees: If you live in a community with an HOA.
These additional costs are often included in an Escrow Account and paid to the lender, who then disburses them to the respective parties. Always factor these into your overall housing budget.
Using the Calculator
Use this calculator to:
Compare different loan scenarios and terms.
Estimate affordability for various home prices.
Understand the impact of interest rates on your monthly payments.
Enter your loan details, click "Calculate Monthly Payment," and see your estimated P&I payment!
var loanAmountInput = document.getElementById('loanAmount');
var interestRateInput = document.getElementById('interestRate');
var interestRateSlider = document.getElementById('interestRateSlider');
var loanTermInput = document.getElementById('loanTerm');
var rateDisplay = document.getElementById('rateDisplay');
var resultLoanAmount = document.getElementById('resultLoanAmount');
var resultInterestRate = document.getElementById('resultInterestRate');
var resultLoanTerm = document.getElementById('resultLoanTerm');
var monthlyPaymentDisplay = document.getElementById('monthlyPayment');
// Link slider to input and update display
interestRateSlider.oninput = function() {
var rate = parseFloat(this.value);
interestRateInput.value = rate.toFixed(2);
rateDisplay.textContent = rate.toFixed(2) + '%';
calculateMortgage(); // Recalculate when slider changes
}
// Update slider and display when input changes
interestRateInput.oninput = function() {
var rate = parseFloat(this.value);
if (isNaN(rate) || rate 100) {
rate = 100;
}
interestRateInput.value = rate.toFixed(2);
interestRateSlider.value = rate.toFixed(2);
rateDisplay.textContent = rate.toFixed(2) + '%';
calculateMortgage();
}
function formatCurrency(amount) {
return "$" + amount.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
function calculateMortgage() {
var principal = parseFloat(loanAmountInput.value);
var annualRate = parseFloat(interestRateInput.value);
var years = parseInt(loanTermInput.value);
// Validate inputs
if (isNaN(principal) || principal <= 0) {
monthlyPaymentDisplay.textContent = "Invalid Amount";
return;
}
if (isNaN(annualRate) || annualRate < 0) {
monthlyPaymentDisplay.textContent = "Invalid Rate";
return;
}
if (isNaN(years) || years <= 0) {
monthlyPaymentDisplay.textContent = "Invalid Term";
return;
}
var monthlyRate = annualRate / 100 / 12;
var numberOfPayments = years * 12;
var monthlyPayment;
if (monthlyRate === 0) {
monthlyPayment = principal / numberOfPayments;
} else {
monthlyPayment = principal * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
if (isNaN(monthlyPayment) || !isFinite(monthlyPayment)) {
monthlyPaymentDisplay.textContent = "Error";
} else {
monthlyPaymentDisplay.textContent = formatCurrency(monthlyPayment);
resultLoanAmount.textContent = formatCurrency(principal);
resultInterestRate.textContent = annualRate.toFixed(2) + "%";
resultLoanTerm.textContent = years + " Years";
}
}
// Initial calculation on page load
window.onload = function() {
calculateMortgage();
};