Buying a home is a significant financial decision, and understanding your mortgage payments is crucial. BECU (Boeing Employees' Credit Union) offers various mortgage options, and this calculator will help you estimate your potential monthly principal and interest payments. This calculation helps you budget effectively and compare different loan scenarios.
How the Mortgage Payment is Calculated
The standard formula for calculating a fixed-rate mortgage payment (P&I – Principal and Interest) is as follows:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
M = Your total monthly mortgage payment (Principal & Interest)
P = The principal loan amount (the amount you borrow)
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)
Example Calculation Breakdown:
Let's consider an example using the calculator inputs:
Loan Amount (P): $300,000
Annual Interest Rate: 4.5%
Loan Term: 30 Years
First, we convert the annual interest rate to a monthly interest rate (i):
4.5% / 12 months = 0.045 / 12 = 0.00375
Next, we calculate the total number of payments (n):
30 years * 12 months/year = 360 payments
Now, we plug these values into the formula:
M = 300000 [ 0.00375(1 + 0.00375)^360 ] / [ (1 + 0.00375)^360 – 1]
M = 300000 [ 0.00375(1.00375)^360 ] / [ (1.00375)^360 – 1]
M = 300000 [ 0.00375 * 3.81401 ] / [ 3.81401 – 1]
M = 300000 [ 0.0143025 ] / [ 2.81401 ]
M = 4290.75 / 2.81401
M ≈ $1,524.80
This calculation estimates a monthly principal and interest payment of approximately $1,524.80.
Important Considerations:
This calculator provides an estimate for the principal and interest (P&I) portion of your mortgage payment. Your actual total monthly housing expense will likely be higher and include:
Property Taxes: Amounts vary significantly by location.
Homeowners Insurance: Required by lenders to protect against damage.
Private Mortgage Insurance (PMI): May be required if your down payment is less than 20%.
HOA Dues: If applicable to your property.
It's always recommended to speak directly with a BECU mortgage specialist to get a precise quote tailored to your financial situation and the specific loan products available. Factors like credit score, down payment, loan type, and current market conditions all play a role.
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 resultDiv = document.getElementById('result');
function updateSliderValue(input, span) {
span.textContent = input.value + (input.id === 'interestRate' ? '%' : ' Years');
var numInputId = input.id.replace('Input', 'NumInput');
var numInput = document.getElementById(numInputId);
if (numInput) {
numInput.value = input.value;
}
}
loanAmountInput.addEventListener('input', calculateMortgage);
interestRateInput.addEventListener('input', function() {
updateSliderValue(this, interestRateValueSpan);
calculateMortgage();
});
interestRateNumInput.addEventListener('input', function() {
interestRateInput.value = this.value;
updateSliderValue(interestRateInput, interestRateValueSpan);
calculateMortgage();
});
loanTermInput.addEventListener('input', function() {
updateSliderValue(this, loanTermValueSpan);
calculateMortgage();
});
loanTermNumInput.addEventListener('input', function() {
loanTermInput.value = this.value;
updateSliderValue(loanTermInput, loanTermValueSpan);
calculateMortgage();
});
function calculateMortgage() {
var P = parseFloat(document.getElementById('loanAmount').value);
var annualRate = parseFloat(document.getElementById('interestRate').value);
var years = parseFloat(document.getElementById('loanTerm').value);
// Input validation
if (isNaN(P) || P <= 0) {
resultDiv.innerHTML = "Please enter a valid loan amount.";
return;
}
if (isNaN(annualRate) || annualRate <= 0) {
resultDiv.innerHTML = "Please enter a valid annual interest rate.";
return;
}
if (isNaN(years) || years <= 0) {
resultDiv.innerHTML = "Please enter a valid loan term in years.";
return;
}
var r = annualRate / 100 / 12; // Monthly interest rate
var n = years * 12; // Number of payments
var monthlyPayment = P * (r * Math.pow(1 + r, n)) / (Math.pow(1 + r, n) – 1);
// Calculate total interest paid
var totalInterest = (monthlyPayment * n) – P;
if (isFinite(monthlyPayment)) {
resultDiv.innerHTML =
'Estimated Monthly P&I: $' + monthlyPayment.toFixed(2) + '' +
'Estimated Total Interest Paid: $' + totalInterest.toFixed(2) + '';
} else {
resultDiv.innerHTML = "Could not calculate mortgage. Please check your inputs.";
}
}
// Initial calculation on page load
calculateMortgage();