This is an estimate for principal and interest only. Property taxes, homeowner's insurance, and PMI are not included.
Understanding Your Washington Mortgage Payment
Calculating your monthly mortgage payment is a crucial step in the home-buying process, especially in Washington State. The primary components determining your payment are the loan amount, the interest rate, and the loan term. Our Washington Mortgage Calculator uses the standard mortgage payment formula to provide an estimate of your principal and interest (P&I) payment.
The Mortgage Payment Formula
The formula used by most mortgage calculators, including this one, is:
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 total amount you borrow, which is the home price minus your down payment)
i = Your monthly interest rate (your annual interest rate divided by 12)
n = The total number of payments over the loan's lifetime (your loan term in years multiplied by 12)
How the Washington Mortgage Calculator Works:
Home Price: Enter the total price of the home you are looking to purchase in Washington.
Down Payment: Input the amount of money you plan to pay upfront. This reduces the principal loan amount.
Loan Term (Years): Select the duration of your mortgage. Common terms in Washington include 15, 20, 30, or even 40 years. Longer terms result in lower monthly payments but higher total interest paid over the life of the loan.
Interest Rate (%): Enter the annual interest rate offered by your lender. This is a critical factor that significantly impacts your monthly payment. Rates can vary based on your credit score, market conditions, and the loan type.
Important Considerations for Washington Homebuyers:
Principal & Interest (P&I): The calculator provides the P&I portion of your payment.
Property Taxes: Washington State has varying property tax rates depending on the county and locality. These will be an additional monthly cost.
Homeowner's Insurance: Lenders require you to have homeowner's insurance, which also adds to your total monthly housing expense.
Private Mortgage Insurance (PMI): If your down payment is less than 20%, you will likely need to pay PMI, which protects the lender in case of default.
HOA Fees: If the property is part of a Homeowners Association, you will have monthly or annual HOA dues.
Washington Specific Programs: Washington State offers various programs for first-time homebuyers, low-to-moderate income borrowers, and veterans that might provide down payment assistance or lower interest rates. Researching these can significantly impact your home-buying affordability.
Use this calculator as a starting point to understand your potential monthly payments. For a precise figure, consult with a mortgage lender who can factor in all associated costs and provide a Loan Estimate.
function calculateMortgage() {
var homePrice = parseFloat(document.getElementById("homePrice").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var loanTerm = parseInt(document.getElementById("loanTerm").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var resultContainer = document.getElementById("resultContainer");
var monthlyPaymentDisplay = document.getElementById("monthlyPayment");
// Input validation
if (isNaN(homePrice) || homePrice <= 0) {
alert("Please enter a valid Home Price.");
return;
}
if (isNaN(downPayment) || downPayment < 0) {
alert("Please enter a valid Down Payment.");
return;
}
if (isNaN(loanTerm) || loanTerm <= 0) {
alert("Please select a valid Loan Term.");
return;
}
if (isNaN(interestRate) || interestRate = homePrice) {
alert("Down payment cannot be greater than or equal to the home price.");
return;
}
var principal = homePrice – downPayment;
var monthlyInterestRate = interestRate / 100 / 12;
var numberOfPayments = loanTerm * 12;
var monthlyPayment = 0;
// Handle case where interest rate is 0 to avoid division by zero
if (monthlyInterestRate === 0) {
monthlyPayment = principal / numberOfPayments;
} else {
var numerator = principal * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments));
var denominator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
monthlyPayment = numerator / denominator;
}
// Check for NaN and Infinity before formatting
if (isNaN(monthlyPayment) || !isFinite(monthlyPayment)) {
monthlyPaymentDisplay.textContent = "$0.00"; // Display 0 or an error message
resultContainer.style.display = "block"; // Show container even for error state if desired
} else {
monthlyPaymentDisplay.textContent = "$" + monthlyPayment.toFixed(2);
resultContainer.style.display = "block";
}
}