A 30-year mortgage is one of the most common home loan options in the United States. It allows homeowners to spread the cost of a home over a long period, making monthly payments more manageable. This calculator helps you estimate your principal and interest (P&I) payment based on the loan amount, interest rate, and the standard 30-year term.
The Math Behind Your Mortgage Payment
The monthly payment for a fixed-rate mortgage is calculated using the following formula:
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 6.5% annual rate is 0.065 / 12 = 0.00541667.
n = The total number of payments over the loan's lifetime. For a 30-year mortgage, this is 30 years * 12 months/year = 360 payments.
How to Use This Calculator:
Loan Amount: Enter the total amount you plan to borrow to purchase your home.
Annual Interest Rate: Input the current annual interest rate offered by your lender. This is a crucial factor affecting your monthly payment.
Loan Term: This calculator is pre-set for a standard 30-year term. The term is fixed at 30 years (360 payments).
Click "Calculate Monthly Payment" to see your estimated P&I payment. Use the "Reset" button to clear the fields and perform a new calculation.
Important Considerations:
This calculator provides an estimate for the principal and interest (P&I) portion of your mortgage payment only. Your actual total monthly housing expense will likely be higher and may include:
Property Taxes: Annual taxes assessed by your local government.
Homeowners Insurance: Required insurance to protect against damage or loss.
Private Mortgage Insurance (PMI): Often required if your down payment is less than 20%.
Homeowners Association (HOA) Fees: If applicable to your property.
Mortgage rates fluctuate daily based on market conditions. The rate you secure will depend on your credit score, loan type, down payment, and lender policies. It's always recommended to shop around with multiple lenders to find the best rates and terms.
function calculateMortgage() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("interestRate").value);
var loanTermYears = 30; // Fixed for this calculator
var numberOfPayments = loanTermYears * 12;
var errorMessages = [];
if (isNaN(loanAmount) || loanAmount <= 0) {
errorMessages.push("Please enter a valid loan amount.");
}
if (isNaN(annualInterestRate) || annualInterestRate 0) {
document.getElementById("result-value").innerHTML = errorMessages.join("");
document.getElementById("result-value").style.color = "red";
document.getElementById("result-value").style.fontSize = "1rem";
return;
}
// Calculate monthly interest rate
var monthlyInterestRate = annualInterestRate / 100 / 12;
// Calculate monthly payment using the mortgage formula
var monthlyPayment = loanAmount * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
// Format the result to two decimal places
var formattedMonthlyPayment = monthlyPayment.toFixed(2);
document.getElementById("result-value").innerHTML = "$" + formattedMonthlyPayment;
document.getElementById("result-value").style.color = "#28a745"; // Success Green
document.getElementById("result-value").style.fontSize = "2.5rem";
}
function resetCalculator() {
document.getElementById("loanAmount").value = "";
document.getElementById("interestRate").value = "";
document.getElementById("result-value").innerHTML = "$0.00";
document.getElementById("result-value").style.color = "#28a745";
document.getElementById("result-value").style.fontSize = "2.5rem";
}