This calculator helps you determine the total amount paid and the effective interest rate when making bi-weekly payments on a loan. Bi-weekly payments can sometimes lead to paying off a loan faster and saving on interest compared to monthly payments, especially if the bi-weekly payment is half of the monthly payment, resulting in one extra monthly payment per year.
function calculateBiWeekly() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTermYears = parseFloat(document.getElementById("loanTermYears").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(loanAmount) || isNaN(annualInterestRate) || isNaN(loanTermYears) || loanAmount <= 0 || annualInterestRate < 0 || loanTermYears <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Calculate monthly payment using the standard loan payment formula
var monthlyRate = annualInterestRate / 100 / 12;
var numberOfMonthlyPayments = loanTermYears * 12;
var monthlyPayment = (loanAmount * monthlyRate) / (1 – Math.pow(1 + monthlyRate, -numberOfMonthlyPayments));
// Bi-weekly payment is half of the monthly payment
var biWeeklyPayment = monthlyPayment / 2;
// Number of bi-weekly payments per year is 26 (52 weeks / 2)
var numberOfBiWeeklyPaymentsPerYear = 26;
// Total number of bi-weekly payments over the loan term
// This calculation implicitly assumes that making 26 bi-weekly payments (half monthly)
// is equivalent to making 13 monthly payments per year (12 + 1 extra).
// The total number of *periods* paid will be slightly less than monthly payments if paid off early.
// However, for comparison, we'll calculate based on the *scheduled* duration.
// A more accurate way to determine loan payoff is iterative, but for a simple bi-weekly comparison,
// we compare total paid based on the *intended* faster payoff.
// Let's calculate the total paid if the loan is paid off by making bi-weekly payments
// equivalent to half of the monthly payment. This results in an extra monthly payment annually.
// The total number of payments made in a year is 26, which is equivalent to 13 monthly payments.
// So the loan term effectively becomes shorter.
var effectiveLoanTermYears = loanAmount / (biWeeklyPayment * numberOfBiWeeklyPaymentsPerYear);
// If the effective term is less than the original term, it means the loan is paid off faster.
// We will calculate the total paid based on the effective payoff.
var actualNumberOfBiWeeklyPayments = Math.ceil(loanAmount / biWeeklyPayment); // Total payments needed to cover principal and interest
var totalPaidBiWeekly = actualNumberOfBiWeeklyPayments * biWeeklyPayment;
var totalInterestPaidBiWeekly = totalPaidBiWeekly – loanAmount;
// To compare apples to apples with monthly payments, let's also calculate total paid for monthly
var totalPaidMonthly = monthlyPayment * numberOfMonthlyPayments;
var totalInterestPaidMonthly = totalPaidMonthly – loanAmount;
var outputHTML = "