Credit Card Interest Calculator
From balance, APR and monthly payment, compute the total interest paid while clearing the debt.
Input Data
Results
At a glance:Revolving credit-card interest accrues when you don't clear the balance in full within the grace period; the bank charges monthly on the outstanding amount. Declining-balance method: monthly interest = balance x APR/12; next balance = balance + interest - payment; sum of interest = total interest. HK credit-card APRs commonly exceed 30% — among the costliest borrowing; if payment ≤ first-month interest, the balance grows forever. WARNING: simplified model; actual interest differs with fees/rate changes. Education, not advice.
Formula
Monthly interest = balance × APR ÷ 12.
Next balance = balance + monthly interest − monthly payment.
Total interest = sum of all monthly interest until balance ≤ 0.
If monthly payment ≤ first-month interest, the balance grows forever (no payoff).
$$I_{t} = B_{t} \\times \\dfrac{\\text{APR}}{12}, \\qquad B_{t+1} = B_{t} + I_{t} - \\text{Payment}$$How to Use
- Enter the current balance.
- Enter the APR.
- Enter the monthly payment to see total interest over repayment.
FAQ
How is credit card interest calculated?
Most cards charge monthly: monthly interest = outstanding balance x APR / 12. If not cleared in full within the grace period, the unpaid part accrues interest monthly and compounds.
How high is a Hong Kong credit card APR?
HK credit-card revolving APRs commonly exceed 30%; the HKMA example uses about 2.5% per month (~35% effective annual). Banks must disclose APR uniformly per the Code of Banking Practice. Although exempt from the moneylenders ordinance, rates should not be extortionate under the Code.
How is the minimum payment calculated, and what if I only pay it?
HK minimum payment is typically 'all interest and fees (incl. annual fee) + at least 1% of principal', or a fixed amount (e.g. HK$50), whichever is higher. Paying only the minimum avoids late fees but reduces principal extremely slowly, stretching repayment over decades with total interest multiple times the principal.
How can I reduce credit card interest?
Most effective: clear in full to use the interest-free period; if you can't, move the balance to a lower-rate personal loan or a 0% balance-transfer promo. Paying more each month also cuts total interest sharply.
Why can't the calculator show total interest?
When the monthly payment is ≤ the first month's interest, the balance grows instead of shrinking and interest accrues without limit — it can never be cleared. Raise the monthly payment above the interest to start reducing principal.
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References
Content review: Calculatorism Finance Team. Results are for reference only; please refer to the relevant authorities for the official figures.