Amortization Calculator with Extra Payment

let amortizationSteps = “”; const currencySymbol = “$”, fixedCurrency = “USD”; function calculateAmortization() { amortizationSteps = “”; const loanAmount = parseFloat(document.getElementById(“loanAmount”).value); const interestRate = parseFloat(document.getElementById(“interestRate”).value) / 100 / 12; const loanTerm = parseFloat(document.getElementById(“loanTerm”).value) * 12; const extraPayment = parseFloat(document.getElementById(“extraPayment”).value); if (isNaN(loanAmount) || isNaN(interestRate) || isNaN(loanTerm) || isNaN(extraPayment) || loanAmount <= 0 || loanTerm <= 0) { alert("Please enter valid positive values for all fields."); return; } const monthlyPayment = (loanAmount * interestRate) / (1 – Math.pow(1 + interestRate, -loanTerm)); const totalPaid = (monthlyPayment + extraPayment) * loanTerm; document.getElementById("monthlyPayment").value = formatCurrency(monthlyPayment); document.getElementById("totalPaid").value = formatCurrency(totalPaid); amortizationSteps += `Inputs:
Loan Amount: ${formatCurrency(loanAmount)}
Annual Interest Rate: ${(interestRate * 100).toFixed(2)}%
Loan Term: ${loanTerm / 12} years
Extra Payment: ${formatCurrency(extraPayment)}

`; amortizationSteps += `Formulas:
Monthly Payment = Loan Amount × Interest Rate / (1 – (1 + Interest Rate) ^ -Loan Term)
Total Paid = (Monthly Payment + Extra Payment) × Loan Term

`; amortizationSteps += `Results:
Monthly Payment: ${formatCurrency(monthlyPayment)}
Total Paid Over Loan Term: ${formatCurrency(totalPaid)}
`; amortizationSteps += `Tip: Making extra payments helps reduce the loan term and interest paid over time.`; if (document.getElementById(“calculationStepsAmortization”).style.display === “block”) { document.getElementById(“calculationStepsAmortization”).innerHTML = amortizationSteps; } } function resetAmortization() { document.querySelectorAll(“#amortization-calculator input”).forEach(el => el.value = “”); amortizationSteps = “”; document.getElementById(“calculationStepsAmortization”).innerHTML = “

Not calculated yet.

“; } function toggleAmortizationSteps() { const s = document.getElementById(“calculationStepsAmortization”); const a = document.getElementById(“toggleArrowAmortization”); if (s.style.display === “none” || s.style.display === “”) { s.style.display = “block”; a.style.transform = “rotate(180deg)”; s.innerHTML = amortizationSteps || “

Not calculated yet.

“; } else { s.style.display = “none”; a.style.transform = “rotate(0deg)”; } } function formatCurrency(n) { return currencySymbol + n.toFixed(2) + ” ” + fixedCurrency; }