Calculate your estimated monthly mortgage payment for a $315,000 loan.
1%5.0%10%
5 Years30 Years30 Years
Estimated Monthly Principal & Interest Payment
$0.00
Understanding Your Mortgage Payment
A mortgage is a significant financial commitment, and understanding how your monthly payment is calculated is crucial. This calculator helps estimate the principal and interest portion of your monthly mortgage payment for a loan amount of $315,000.
The Mortgage Payment Formula
The standard formula used to calculate a fixed-rate mortgage payment is the annuity formula:
$$ M = P \left[ \frac{i(1+i)^n}{(1+i)^n – 1} \right] $$
Where:
M = Your total monthly mortgage payment (Principal and Interest)
P = The principal loan amount (in this case, $315,000)
i = Your monthly interest rate. This is your annual interest rate divided by 12. For example, if your annual rate is 5%, your monthly rate is 0.05 / 12 = 0.0041667.
n = The total number of payments over the loan's lifetime. This is your loan term in years multiplied by 12. For a 30-year loan, this would be 30 * 12 = 360 payments.
How the Calculator Works
This calculator takes the following inputs:
Loan Amount: The total amount you are borrowing. For this calculator, it's fixed at $315,000.
Annual Interest Rate: The yearly rate charged by the lender. You can adjust this using the slider or by typing directly.
Loan Term (Years): The duration of the loan, typically 15, 20, or 30 years. This determines the total number of monthly payments.
The calculator then applies the formula above to compute your estimated monthly payment.
Important Considerations
Principal and Interest (P&I) Only: This calculator estimates only the principal and interest portion of your payment. Your actual total monthly housing expense will likely be higher, including:
Property Taxes: Paid to your local government.
Homeowner's Insurance: Required by lenders to protect against damage.
Private Mortgage Insurance (PMI): Often required if your down payment is less than 20%.
HOA Fees: If you live in a community with a Homeowners Association.
Estimates: The figures generated are estimates. Actual loan terms, fees, and lender calculations may vary. It's always recommended to consult with a mortgage lender for a precise quote.
var loanAmountInput = document.getElementById('loanAmount');
var interestRateInput = document.getElementById('interestRate');
var interestRateValueSpan = document.getElementById('interestRateValue');
var interestRateNumInput = document.getElementById('interestRateNum');
var loanTermInput = document.getElementById('loanTerm');
var loanTermValueSpan = document.getElementById('loanTermValue');
var loanTermNumInput = document.getElementById('loanTermNum');
var monthlyPaymentSpan = document.getElementById('monthlyPayment');
// Update display for sliders
interestRateInput.oninput = function() {
var value = parseFloat(this.value).toFixed(1);
interestRateValueSpan.textContent = value + '%';
interestRateNumInput.value = value; // Update hidden number input
calculateMortgage();
}
interestRateNumInput.oninput = function() {
var value = parseFloat(this.value);
if (value >= 1 && value = 5 && value <= 30) {
loanTermInput.value = value;
loanTermValueSpan.textContent = value + ' Years';
calculateMortgage();
} else {
alert("Please enter a loan term between 5 and 30 years.");
this.value = loanTermInput.value; // Reset to valid value
}
}
function calculateMortgage() {
var principal = parseFloat(loanAmountInput.value);
var annualInterestRate = parseFloat(interestRateInput.value);
var loanTermYears = parseInt(loanTermInput.value);
if (isNaN(principal) || isNaN(annualInterestRate) || isNaN(loanTermYears)) {
monthlyPaymentSpan.textContent = "Invalid Input";
return;
}
if (principal <= 0 || annualInterestRate <= 0 || loanTermYears <= 0) {
monthlyPaymentSpan.textContent = "Inputs must be positive";
return;
}
var monthlyInterestRate = annualInterestRate / 100 / 12;
var numberOfPayments = loanTermYears * 12;
var monthlyPayment = principal * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
if (isNaN(monthlyPayment) || !isFinite(monthlyPayment)) {
monthlyPaymentSpan.textContent = "Calculation Error";
return;
}
monthlyPaymentSpan.textContent = "$" + monthlyPayment.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
}
// Initial calculation on page load
document.addEventListener('DOMContentLoaded', function() {
calculateMortgage();
});