Compare an extra payment as a repeated commitment
A $3,000 balance at 18% APR takes 41 modeled monthly payments at $100. Adding $50 every month changes the payment to $150 and the estimate to 24 months. The difference is 17 monthly payments; the first-month interest is $45 in either path because both begin with the same balance.
The lower-interest result depends on keeping the larger payment in later months, not merely making one larger payment today. This calculator’s Extra monthly payment field models a repeated extra amount, not a one-time lump sum.
Check the amount against the months it needs to last
- Use a current balance and the applicable APR. Enter the monthly amount you would otherwise maintain as the base payment.
- Review your own budget for irregular bills and months with lower income. The calculator cannot decide how much you can afford.
- Enter a proposed extra amount separately. Read the two payoff paths and the modeled interest difference together.
- If the amount depends on a temporary expense cut, check whether that cut lasts as long as the payment scenario.
- Confirm your lender’s payment application and account terms before acting. Keep a record of what actually happens to the balance.
If your plan frees $50 only for the next six months, entering $50 as a permanent extra amount overstates that commitment. This tool does not switch payments after month six. Treat its output as a constant-payment comparison, not a schedule for a changing budget.
Read unavailable comparisons correctly
If the base payment does not exceed modeled monthly interest, the base path cannot decline. A larger combined payment may still repay the balance, but there is no finite baseline payoff from which to subtract months or total interest. The tool explains that situation instead of inventing a savings number.
At 0% APR, a larger payment can shorten the modeled timeline without reducing interest, because both paths already have zero interest. When a payment is large enough to clear the balance in one month, adding more does not make it zero months; the final payment is capped at the amount owed.
Changing APRs, fees and daily-interest rules are outside the model. For auto loans, the CFPB recommends checking contract terms for prepayment penalties. An account-specific payoff quote remains separate from this estimate.
Example arithmetic checked against our calculator. Educational estimates; changing prices and personal circumstances can change results.