Student Loan Calculator

Standard fixed-rate student loans rely on an amortization formula to ensure your debt is fully paid off by the end of the term. The core equation calculates your fixed monthly payment using your principal loan balance (P), monthly interest rate (r), and total repayment term in months (n): monthly_payment = P * (r / 12) / (1 - (1 + (r / 12)) ^ (-n)). Once your monthly payment is established, you can find the cumulative lifetime cost by multiplying the monthly payment by the total number of months, yielding your total amount paid. Subtracting your original loan balance from this total amount reveals your total interest paid. Finally, dividing the total interest paid by the total amount paid gives you the exact interest percentage of your overall investment.

Imagine you graduate with a student loan balance of $35,000 at a fixed annual interest rate of 6% (or 0.06) over a standard 10-year repayment term, which equals 120 months. First, we find the monthly interest rate by dividing 0.06 by 12, resulting in 0.005. Next, we apply the amortization formula: monthly_payment = 35000 * 0.005 / (1 - (1 + 0.005) ^ (-120)). This evaluates to 175 / (1 - (1.005)^(-120)) or roughly 175 / (1 - 0.548811), yielding a monthly payment of $388.57. Over 120 months, your total amount paid will be $388.57 * 120 = $46,628.40. Subtracting the original $35,000 balance shows you will pay $11,628.40 in total interest, meaning interest accounts for about 24.9% of your total payments.

Making small additional principal payments each month can drastically reduce your total interest and shorten your repayment timeline. Always prioritize paying off high-interest private loans before tackling federal loans that might offer income-driven repayment options or forgiveness programs. Regularly review your loan statements to ensure servicers apply your payments correctly toward the principal balance rather than future months' bills.