Your Estimated Monthly Payment (Principal & Interest):
$0.00
(Excludes property taxes, homeowner's insurance, and HOA fees)
Understanding Your Seattle Mortgage Payment
Purchasing a home in Seattle, a vibrant and growing metropolitan area, is a significant financial undertaking. Understanding how your mortgage payment is calculated is crucial for budgeting and financial planning. This calculator helps estimate the principal and interest portion of your monthly mortgage payment.
The Math Behind the Mortgage Payment
The most common formula used to calculate a fixed-rate mortgage's monthly payment (M) is the annuity formula:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
P = Principal Loan Amount (This is your Home Price minus your Down Payment).
i = Monthly Interest Rate (This is your Annual Interest Rate divided by 12).
n = Total Number of Payments (This is your Loan Term in years multiplied by 12).
Key Factors in Your Mortgage Calculation:
Home Price: The total cost of the property you intend to buy.
Down Payment: The initial amount of money you pay upfront. A larger down payment reduces the principal loan amount, lowering your monthly payments and potentially the interest paid over time. In Seattle, due to high property values, a substantial down payment is often necessary.
Loan Term: The duration over which you will repay the loan, typically 15 or 30 years for fixed-rate mortgages. Shorter terms mean higher monthly payments but less total interest paid.
Annual Interest Rate: The yearly percentage charged by the lender. This is influenced by market conditions, your credit score, and the loan type. Even small differences in interest rates can significantly impact your monthly payment and the total cost of the loan over its lifetime.
What's Included and What's Not:
This calculator provides an estimate for Principal and Interest (P&I) only. Your actual total monthly housing cost in Seattle will likely be higher and typically includes:
Property Taxes: These vary by location and property value. Seattle and King County have specific tax rates.
Homeowner's Insurance: Required by lenders to protect against damage to the property.
Private Mortgage Insurance (PMI): If your down payment is less than 20%, you may be required to pay PMI.
HOA Fees: If you are buying a condominium or a property in a managed community, you'll have monthly Homeowners Association fees.
It's essential to factor in these additional costs when determining your total housing affordability in the competitive Seattle real estate market.
Using the Calculator:
Simply enter the estimated home price, your planned down payment percentage, the desired loan term in years, and the annual interest rate. Click "Calculate Monthly Payment" to see an estimate of your P&I payment.
This tool is designed to provide a quick estimate. For precise figures and to discuss loan options tailored to the Seattle market, consult with a qualified mortgage lender or financial advisor.
function calculateMortgage() {
var homePrice = parseFloat(document.getElementById("homePrice").value);
var downPaymentPercent = parseFloat(document.getElementById("downPayment").value);
var loanTermYears = parseFloat(document.getElementById("loanTerm").value);
var annualInterestRate = parseFloat(document.getElementById("interestRate").value);
var principal = 0;
var monthlyPayment = 0;
var resultText = "$0.00";
if (isNaN(homePrice) || homePrice <= 0) {
alert("Please enter a valid Home Price.");
return;
}
if (isNaN(downPaymentPercent) || downPaymentPercent 100) {
alert("Please enter a valid Down Payment percentage (0-100).");
return;
}
if (isNaN(loanTermYears) || loanTermYears <= 0) {
alert("Please enter a valid Loan Term in years.");
return;
}
if (isNaN(annualInterestRate) || annualInterestRate 0) {
monthlyPayment = principal * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments)) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
} else {
// Handle case for 0% interest rate
monthlyPayment = principal / numberOfPayments;
}
if (isNaN(monthlyPayment) || monthlyPayment < 0) {
resultText = "Calculation Error";
} else {
resultText = "$" + monthlyPayment.toFixed(2);
}
document.getElementById("monthlyPayment").innerText = resultText;
}