Loan Repayment Calculator

About the Loan Repayment Calculator

A loan repayment calculator works backwards from your desired monthly payment to tell you exactly how long it will take to pay off any loan — and how much total interest you will pay in the process. Unlike a standard loan calculator that fixes the term and finds the payment, a repayment calculator lets you set the payment amount and finds the payoff timeline. This reverse approach is more useful for people who are managing a specific monthly budget and want to know the consequences: if I pay $600/month on this $25,000 loan at 8%, when will it be gone? Our free repayment calculator works for any type of loan — personal loans, car loans, student loans, credit card balances, or any debt with a fixed interest rate. Enter your current balance, interest rate, and desired monthly payment to instantly see the payoff date, total months, total interest paid, and total amount paid. The calculator also warns you if your payment is too low to ever pay off the loan — a critically important check for people paying credit card minimums.

How It Works

The payoff timeline formula is derived from the present value of annuity equation solved for n: Months to payoff = -ln(1 - P×r/PMT) / ln(1+r), where P is the loan balance, r is the monthly interest rate (annual rate / 12), and PMT is the monthly payment. Critical constraint: PMT must exceed P × r (the monthly interest charge) or the loan never pays off. Example: $20,000 loan at 8% annual rate, $500/month payment. Monthly r = 0.08/12 = 0.006667. Monthly interest = $20,000 × 0.006667 = $133.33. Since $500 > $133.33, the loan can be paid off. n = -ln(1 - 20,000 × 0.006667 / 500) / ln(1.006667) = -ln(1 - 0.2667) / 0.006645 = -ln(0.7333) / 0.006645 = 0.3101 / 0.006645 = 46.7 months — approximately 3.9 years. Total paid: approximately $23,350. Total interest: $3,350. Adding $100/month extra ($600 total): n = -ln(1 - 20,000 × 0.006667 / 600) / ln(1.006667) = 37.5 months. Saves 9 months and approximately $800 in interest — demonstrating how modest extra payments compound significantly.

Tips & Best Practices

• ✓Always check the minimum viable payment before setting a repayment target: for a $30,000 loan at 12% APR, the minimum monthly interest is $300. Any payment at or below $300/month means the balance grows — never shrinks. The calculator flags this automatically.
• ✓Rounding up your payment to the next hundred dollars is an underrated strategy: on a $15,000 auto loan at 6.5%, rounding from $293 to $300/month saves 3 months and $190 in interest with minimal budget impact.
• ✓Bi-weekly payment strategy for simple interest loans: paying half your monthly payment every two weeks results in 26 half-payments (13 full monthly equivalents) per year. On a $25,000 personal loan at 8%, this strategy saves approximately 10 months.
• ✓High-rate first (avalanche method): if you have multiple debts, direct extra monthly budget to the highest-rate balance first while paying minimums on all others. This minimizes total interest mathematically. The calculator helps you model the payoff timeline for each debt individually.
• ✓Income-driven student loan repayment: federal student loan plans (IBR, SAVE, PAYE) set payments as a percentage of discretionary income rather than a fixed amount. These are not modeled here — use the federal studentaid.gov Loan Simulator for income-driven plan projections.
• ✓Refinancing versus extra payments: if your current rate is above prevailing rates, refinancing to a lower rate can reduce total interest more than extra payments. Model both: current loan with extra payments versus refinanced loan at lower rate with standard payments.
• ✓Debt snowball versus avalanche: the avalanche (highest rate first) saves more mathematically. The snowball (lowest balance first) provides psychological wins through faster payoffs and higher success rates behaviorally. The calculator helps you model either approach.

Who Uses This Calculator

Borrowers with existing loans setting a budget-based monthly payment and determining their payoff timeline. People evaluating whether they can afford to pay off a loan in a specific number of months. Anyone trying to understand the tradeoff between a higher monthly payment (faster payoff, less interest) and a lower payment (easier budget, more interest). Financial coaches helping clients visualize the impact of different payment amounts on debt freedom dates.