Model cumulative credit card interest when you make a fixed payment and stop adding new charges. The tool applies daily compounding to equal-length monthly periods, then subtracts your payment. It reports interest, payment count, and the final payment separately.
Your interest schedule
| Payment | Amount paid | Interest | Balance | Cumulative interest |
|---|
Worked example: source inputs in a single-balance model
CFPB payment-allocation examples include a $500 cash advance balance at 20% APR and a $400 excess payment. Here those figures are reused only as balance, rate, and fixed payment inputs for a separate single-balance projection. No other balance, fees, or minimum payment is modeled. Outputs below are calculated with the formula above; they are not results published in the CFPB allocation example.
| Payments to payoff | Interest | Final payment |
|---|---|---|
| 2 | $10.22 | $110.22 |
How it works
d = APR / 100 / 365
g = (1 + d)^(365 / 12) - 1
Period interest = opening balance * g
Payment = min(fixed payment, balance + interest)
Closing balance = balance + interest - payment
The CFPB daily periodic rate explanation describes daily accrual and compounding and notes that issuers may use a different day-count basis. This model uses the specified basis, splits a year into equal monthly periods, and applies each payment at the period end. Sum the period interest amounts for cumulative interest. This is an illustrative recurrence, not a reproduction of a particular card agreement.
What fixed payment means
A fixed payment is the same chosen dollar amount in each modeled period until the balance can be paid in full. The last payment is limited to the outstanding balance plus that period's modeled interest. This is different from a changing minimum payment formula. Enter the amount you intend to pay, rather than assuming that a statement minimum will remain unchanged as the balance declines.
The schedule shows interest charged in each period and a separate cumulative interest column. The cumulative amount is a running sum. The total paid combines repayment of the starting balance with modeled interest. If the starting balance is already zero, the result shows no payments and no interest. If a payment fails to cover modeled interest, the tool reports that condition instead of suggesting a payoff date.
Why a real card statement can differ
The CFPB explains that some issuers calculate daily interest and add it to the prior day's balance. Actual statement calculations depend on the issuer's agreement, transaction timing, and payment posting. This tool smooths the year into equal monthly periods. Real billing cycles have their own dates, so a payment count here describes modeled periods rather than a dated statement schedule.
The model assumes a single starting balance at a single fixed APR. It excludes new purchases, cash advance fees, balance transfer fees, promotional rates, deferred interest, and additional balances with other rates. A grace period can also change whether interest applies. These exclusions are why a useful comparison inside this tool does not necessarily reproduce the amount owed on a specific statement.
Use the schedule to compare your assumptions
Keep the starting balance and APR unchanged and calculate a different fixed payment to compare cumulative interest under the same model. Check both the total interest and the final payment. A partial last payment is expected because the chosen fixed amount can exceed the balance remaining at the end of the schedule.
For statement reconciliation, use the actual daily balances, cycle lengths, payment dates, and calculation method in your card agreement. The tool's annual grouping and fixed-rate loan pages do not replace those records. For a fixed-term installment loan, use the cumulative interest calculator instead; for savings growth, use cumulative interest earned. These tools deliberately ask different inputs because the cash flows differ.
Frequently asked questions
What if my payment is too small?
The calculator rejects a payment that does not cover modeled interest. It also reports if payoff would exceed its calculation limit.
Will this match my credit card statement?
Only a calculation using the agreement's method, daily balances, actual cycle lengths, and posting dates can reconcile a specific statement.
Sources
Data as of 2026-10-05. Source examples and formula documentation only; no live market rates.