Calculator
Balance over time
Example data table
| Scenario | Balance | APR | Payment | Extra | Annual Fee | Est. Payoff |
|---|---|---|---|---|---|---|
| Base plan | $45,000 | 9.250% | $900 | $0 | $75 | ~70 months |
| With extra principal | $45,000 | 9.250% | $900 | $150 | $75 | ~55 months |
| Extra + lump sum | $45,000 | 9.250% | $900 | $150 | $75 | ~48 months |
Formula used
- Monthly rate: r = APR ÷ 12
- Monthly interest: Interest = Balance × r
- Monthly fee (if any): Fee = Annual Fee ÷ 12
- Principal paid: Principal = Payment − Interest − Fee
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Payment level drives payoff speed
Payoff time is dominated by how much cash reaches principal each month. With a $45,000 balance at 9.25% APR, a $900 payment can take roughly 70 months, while adding $150 extra can reduce the timeline to about 55 months. The difference comes from compounding: earlier principal reductions shrink future interest, so later payments work harder.
For planning, test at least three payment levels: minimum required, your typical amount, and a stretch target. If the calculator flags stalled payoff, raise payment above monthly interest plus fees. Even small increases can shift payoff by many months. and save thousands.
APR changes interest accumulation quickly
A one‑point APR move can materially change total interest. On a $45,000 balance, 8.25% vs 9.25% increases the first‑month interest by about $37.50 (because $45,000 × 0.01 ÷ 12). If payments stay constant, higher APR shifts more of each payment to interest, delaying the payoff date.
Fees behave like hidden interest
Annual fees reduce principal capacity. A $75 annual fee is $6.25 per month; that amount must be covered before principal drops. Over five years, that alone totals $375, and it also increases interest slightly by slowing balance reduction. If your line has recurring fees, include them to avoid optimistic timelines.
Interest‑only periods postpone principal reduction
During an interest‑only phase, the required payment typically covers interest (and any fee) but not principal. If you set 12 interest‑only months and pay only interest, the balance stays near $45,000 for a full year, and the payoff clock effectively starts later. Adding an “extra principal” amount during this phase is the fastest way to offset the delay.
Lump sums create step‑changes in payoff date
One‑time payments create immediate balance drops that compound forward. For example, a $5,000 lump sum in month 6 reduces interest from that point onward by about $38.54 per month at 9.25% (5,000 × 0.0925 ÷ 12). The schedule export helps compare “extra monthly” versus “lump sum” strategies using the same baseline assumptions.
FAQs
What payment should I enter if my line requires interest-only now?
Enter your expected post‑interest payment in “Monthly payment,” then set “Interest‑only months.” Add any principal you plan to pay during that phase in “Extra monthly principal.”
Why does the calculator warn that payoff will not decline?
Your payment is not covering monthly interest plus fees, so principal cannot fall. Increase the payment, add extra principal, lower fees, or reduce APR assumptions until principal becomes positive.
Does the schedule assume variable rates?
No. The simulation uses a fixed APR you enter and applies a monthly rate equal to APR ÷ 12. If your rate can change, run multiple scenarios to bracket best, expected, and worst cases.
How are annual fees handled?
Annual fees are converted to a monthly amount (annual ÷ 12) and added to the monthly cost before principal is calculated. This makes payoff estimates more conservative when your line charges recurring fees.
When is a lump sum applied?
The lump sum is applied at the start of the selected month as a direct principal reduction. The remaining payment for that month is then processed normally, and future interest is computed on the lower balance.
Can I use this to compare refinancing or fixed loans?
Yes for rough comparisons. Enter the refinance balance and rate, then use the same payment level. Differences in compounding rules and closing costs are not modeled, so add those separately in your decision.
The calculator runs these steps month-by-month until the balance reaches zero or the max-month limit is hit.
How to use this calculator
- Enter your current balance and annual rate.
- Add your monthly payment and any extra principal.
- Include fees and interest-only months if needed.
- Optionally add a lump-sum month and amount.
- Click Calculate Payoff Time to see results above.
- Use export buttons to download your schedule.
This tool is for planning and comparison, not financial advice.