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Categories: Calculator , Finance
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Credit card balances accrue compound interest that snowballs when repayments barely meet the minimum. Key factors include outstanding balance, annual percentage rate (APR), repayment frequency, and any new charges. Grasping how these elements combine lets you forecast costs, optimise payments, and regain control before interest silently erodes purchasing power over months or years.

Basing your figures on real balances, the calculator models each monthly cycle: new charges are added, interest accrues at a periodic rate, and your chosen payment splits between interest and principal. It repeats the cycle until the balance reaches zero, then totals months required, interest paid, and overall cash outlay, updating interactive charts instantly.

Suppose you carry a $5,000 balance at 18 % APR and increase the monthly payment from $150 to $200; the tool shows you could be debt-free nearly a year sooner and save hundreds in interest. Debt projections assume consistent behaviour; unexpected fees or missing payments extend payoff time and increase costs.

Technical Details:

Credit card amortisation traces the declining balance of revolving debt under compound interest. Each billing cycle charges interest on the current balance at a nominal annual percentage rate converted to a periodic rate r = APR / 12 / 100. When the cardholder pays more than the interest accrued, the remainder reduces principal, shortening the repayment period. Consistent modelling requires capturing any additional monthly charges and optional extra repayments to reflect realistic behaviour.

r=APR1200 In=Bn-1×r Pn=Payment−In Bn=Bn-1+Charges−Pn
MonthsPay-off Outlook
0 – 12Rapid clearance
13 – 36Controlled repayment
37 – 60Extended repayment
> 60Prolonged debt

Shorter horizons lower total interest and free available credit sooner, whereas longer horizons inflate costs and heighten default risk.

  • Balance – outstanding principal at statement close.
  • APR – annual percentage rate applied to the balance.
  • Monthly payment – planned minimum repayment.
  • Extra payment – voluntary amount added each month.
  • New charges – fresh spending posted every cycle.

Example (Balance =$5 000, APR = 18 %, Payment =$150):

r=181200=0.015 I1=5000×0.015=75 P1=150−75=75 B1=5000−75=4925

The cycle repeats until Bn reaches zero.

  • No daily compounding; the model assumes monthly posting.
  • Interest rate remains constant for the entire horizon.
  • No late fees, penalty rates, or promotional offers are included.
  • Payments occur on the same calendar day each cycle.
  • Zero or negative payments abort the calculation.
  • Payment less than first-cycle interest triggers a warning.
  • Balances over 999 999 may cause numeric rounding drift.
  • APR above 100 % yields unrealistic projections.

Standard amortisation logic matches methods outlined in Consumer Financial Protection Bureau guidance and peer-reviewed studies on revolving credit behaviour.

Calculations occur entirely in your browser; no financial data is transmitted or stored.

Step-by-Step Guide:

Follow these steps to project your pay-off timeline and interest cost.

  1. Enter your current balance in currency units.
  2. Input the APR expressed as an annual percentage.
  3. Specify the monthly payment you plan to make.
  4. (Optional) Add Extra payment or New charges to reflect planned behaviour.
  5. Review the payoff time, interest cost, amortisation schedule, and charts that appear below the form.

FAQ:

Why is my payoff longer than expected?

The interest portion is larger when the balance is high; unless payments rise, progress is slower at the start.

What happens if I add new charges?

New spending increases the balance before interest is calculated, extending the payoff horizon and total cost.

Is my data stored?

No. All inputs remain inside your browser session; refreshing clears them.

Does the tool use daily compounding?

No. It applies interest once per monthly cycle for clarity; actual statements may compound daily.

Can I export the schedule?

Yes. Use the “Download CSV” button to save the full amortisation table for offline analysis.

Glossary:

APR
Annual rate that defines interest cost.
Principal
Portion of payment reducing balance.
Interest
Charge applied for borrowing money.
Amortisation
Structured reduction of debt over time.
CSV
Comma-separated file for tabular data.

No financial data leaves your device.