Your Estimated Monthly Mortgage Payment (Principal & Interest):
$0.00
Understanding Your Mortgage Payment
This calculator helps you estimate your monthly mortgage payment, specifically the principal and interest (P&I) portion. It uses the standard formula for calculating annuity payments, which is commonly used for mortgages. Understanding this calculation is crucial for budgeting and making informed decisions when buying a home.
The factors that influence your monthly P&I payment are:
Loan Amount: The total amount of money you are borrowing to purchase the property. A larger loan amount will result in higher monthly payments.
Annual Interest Rate: The yearly cost of borrowing money, expressed as a percentage. A higher interest rate increases your monthly payment. Mortgage rates fluctuate based on market conditions and your creditworthiness.
Loan Term: The total duration of the loan, typically expressed in years (e.g., 15, 30 years). A longer loan term will result in lower monthly payments but you'll pay more interest over the life of the loan.
The Formula:
The monthly mortgage payment (M) is calculated using the following formula:
Therefore, the estimated monthly principal and interest payment for a $300,000 loan at 5% for 30 years would be approximately $1,610.46.
Important Note: This calculator provides an estimate for Principal and Interest (P&I) only. Your actual monthly mortgage payment may be higher as it often includes other costs such as property taxes, homeowner's insurance, and potentially Private Mortgage Insurance (PMI) or Homeowner Association (HOA) fees. These additional costs are often bundled into an escrow account and paid as part of your total monthly housing expense.
function calculateMortgage() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTermYears = parseFloat(document.getElementById("loanTermYears").value);
var resultDiv = document.getElementById("result");
var resultValueDiv = document.getElementById("result-value");
if (isNaN(loanAmount) || isNaN(annualInterestRate) || isNaN(loanTermYears) ||
loanAmount <= 0 || annualInterestRate < 0 || loanTermYears <= 0) {
resultDiv.style.display = "none";
alert("Please enter valid positive numbers for all fields.");
return;
}
var monthlyInterestRate = annualInterestRate / 12 / 100;
var numberOfPayments = loanTermYears * 12;
var monthlyPayment = 0;
// Handle case where interest rate is 0
if (monthlyInterestRate === 0) {
monthlyPayment = loanAmount / numberOfPayments;
} else {
monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
}
if (isNaN(monthlyPayment) || !isFinite(monthlyPayment)) {
resultDiv.style.display = "none";
alert("Calculation error. Please check your inputs.");
return;
}
resultValueDiv.textContent = "$" + monthlyPayment.toFixed(2);
resultDiv.style.display = "block";
}