The monthly payment for a house, also known as a mortgage payment, is typically composed of four main parts: Principal, Interest, Taxes, and Insurance (often abbreviated as PITI). However, this calculator focuses on the Principal and Interest (P&I) portion, which is the core of your loan repayment.
The calculation for the Principal and Interest (P&I) monthly payment is based on a standard loan amortization formula. It determines a fixed monthly payment amount that will gradually pay down the loan's principal balance while also covering the interest accrued over the loan's lifetime.
The formula used 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 (House Price – Down Payment)
i = Your monthly interest rate (Annual Interest Rate / 12 / 100)
n = The total number of payments (Loan Term in Years * 12)
How to Use This Calculator:
House Price: Enter the total cost of the house you are looking to purchase.
Down Payment: Enter the amount of money you plan to pay upfront. This reduces the loan amount.
Annual Interest Rate: Input the yearly interest rate offered by your lender (e.g., 5.5 for 5.5%).
Loan Term (Years): Specify how many years you plan to take to repay the loan (e.g., 15, 30).
Click "Calculate Payment" to see your estimated monthly Principal and Interest payment.
Important Note: This calculator provides an estimate for the Principal and Interest (P&I) portion only. Your actual total monthly housing payment will likely be higher as it typically includes property taxes, homeowner's insurance premiums, and potentially Private Mortgage Insurance (PMI) or Homeowner Association (HOA) fees. These additional costs, often referred to as PITI, vary significantly based on your location, insurance choices, and specific property. It's crucial to consult with your lender or a financial advisor for a complete picture of all housing expenses.
function calculateMonthlyPayment() {
var principalInput = document.getElementById("principal");
var downPaymentInput = document.getElementById("downPayment");
var interestRateInput = document.getElementById("interestRate");
var loanTermInput = document.getElementById("loanTerm");
var monthlyPaymentDisplay = document.getElementById("monthlyPayment");
var principal = parseFloat(principalInput.value);
var downPayment = parseFloat(downPaymentInput.value);
var annualInterestRate = parseFloat(interestRateInput.value);
var loanTerm = parseFloat(loanTermInput.value);
// Clear previous error messages if any
monthlyPaymentDisplay.style.color = "#28a745"; // Reset to success green
monthlyPaymentDisplay.textContent = "$0.00";
// Input validation
if (isNaN(principal) || principal <= 0) {
monthlyPaymentDisplay.textContent = "Please enter a valid House Price.";
monthlyPaymentDisplay.style.color = "#dc3545"; // Red for error
return;
}
if (isNaN(downPayment) || downPayment principal) {
monthlyPaymentDisplay.textContent = "Down payment cannot be more than the house price.";
monthlyPaymentDisplay.style.color = "#dc3545";
return;
}
if (isNaN(annualInterestRate) || annualInterestRate <= 0) {
monthlyPaymentDisplay.textContent = "Please enter a valid Annual Interest Rate.";
monthlyPaymentDisplay.style.color = "#dc3545";
return;
}
if (isNaN(loanTerm) || loanTerm 0) {
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
} else {
// Handle case where interest rate is 0 (unlikely for mortgages but good practice)
monthlyPayment = loanAmount / numberOfPayments;
}
// Display the result, formatted as currency
if (isFinite(monthlyPayment)) {
monthlyPaymentDisplay.textContent = "$" + monthlyPayment.toFixed(2);
} else {
monthlyPaymentDisplay.textContent = "Calculation Error";
monthlyPaymentDisplay.style.color = "#dc3545";
}
}