How to Calculate Unknown Interest Rate in Excel

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Mortgage Refinance Savings Calculator

Calculate your monthly savings and see how long it takes to break even on your refinance costs.

Current Monthly Payment (P&I): $0.00
New Monthly Payment (P&I): $0.00
Monthly Savings: $0.00
Break-Even Point: 0 Months
Total Savings Over New Term: $0.00

How Does a Mortgage Refinance Save You Money?

Refinancing involves replacing your current mortgage with a new loan, typically to secure a lower interest rate or change the loan term. By lowering your interest rate, you reduce the cost of borrowing, which directly lowers your monthly principal and interest (P&I) payment.

Understanding the Break-Even Point

While a lower monthly payment is attractive, refinancing isn't free. You will encounter closing costs, which usually range from 2% to 5% of the loan amount. The Break-Even Point is the number of months it takes for your monthly savings to "pay back" those closing costs. If you plan to move before hitting your break-even point, refinancing might actually cost you money.

Example Calculation

Suppose you have a $300,000 balance at a 6.5% interest rate. Your current monthly payment is roughly $1,896. If you refinance into a new 30-year loan at 4.5%, your new payment would be approximately $1,520.

  • Monthly Savings: $376
  • Closing Costs: $5,000
  • Break-Even Point: $5,000 / $376 = 13.3 months

In this scenario, after 14 months, the refinance has paid for itself, and every month thereafter is pure profit.

When Should You Consider Refinancing?

Most experts suggest that if you can lower your interest rate by at least 0.75% to 1%, refinancing is worth investigating. However, you should also consider:

  • Loan Duration: If you restart a 30-year clock after already paying 10 years on your old loan, you might pay more in total interest even with a lower rate.
  • Equity: Having at least 20% equity can help you avoid Private Mortgage Insurance (PMI) on the new loan.
  • Credit Score: A higher credit score since you took out your original loan may qualify you for significantly better rates.
function calculateRefiSavings() { var balance = parseFloat(document.getElementById('currentBalance').value); var oldRate = parseFloat(document.getElementById('currentRate').value) / 100 / 12; var newRate = parseFloat(document.getElementById('newRate').value) / 100 / 12; var termYears = parseFloat(document.getElementById('newTerm').value); var costs = parseFloat(document.getElementById('closingCosts').value); if (isNaN(balance) || isNaN(oldRate) || isNaN(newRate) || isNaN(termYears) || isNaN(costs)) { alert("Please enter valid numbers in all fields."); return; } // Monthly payment formula: P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ] // For old payment, we assume the user wants to compare current monthly obligation against the new one // Note: Old payment calculation here assumes the balance is treated as a new loan for comparison // or the user is looking at the immediate payment difference. var n = termYears * 12; var oldPayment = balance * (oldRate * Math.pow(1 + oldRate, n)) / (Math.pow(1 + oldRate, n) – 1); var newPayment = balance * (newRate * Math.pow(1 + newRate, n)) / (Math.pow(1 + newRate, n) – 1); var monthlySavings = oldPayment – newPayment; var breakEvenMonths = costs / monthlySavings; var totalSavings = (monthlySavings * n) – costs; // Formatting document.getElementById('oldPaymentDisplay').innerText = "$" + oldPayment.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('newPaymentDisplay').innerText = "$" + newPayment.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('monthlySavingsDisplay').innerText = "$" + monthlySavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); if (monthlySavings > 0) { document.getElementById('breakEvenDisplay').innerText = breakEvenMonths.toFixed(1) + " Months"; document.getElementById('totalSavingsDisplay').innerText = "$" + totalSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); } else { document.getElementById('breakEvenDisplay').innerText = "Never (New rate is higher)"; document.getElementById('totalSavingsDisplay').innerText = "$0.00"; } document.getElementById('refiResults').style.display = 'block'; }

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