Finance & Money
Credit Card Interest Calculator
Estimate monthly periodic rate, first-month interest, first-month balance reduction, payoff months, payoff interest, card cost with annual fees, and months saved by a comparison payment.
Monthly periodic rate-
Estimated first-month interest-
First-month payment less interest and new charges-
Estimated payoff time without new charges-
Estimated payoff interest-
Modeled interest plus annual fees over payoff-
Payoff time at comparison payment-
Months saved at comparison payment-
Decision view
Credit card fixed-payment payoff staircase
Credit card fixed-payment payoff staircaseThe planned and comparison fixed-payment payoff lanes keep balance, months, interest, and months saved separate.
Exact scenario comparisonPlanned monthly payment changes while all other entered assumptions remain constant.
| Planned monthly payment | Monthly periodic rate | Estimated first-month interest | First-month payment less interest and new charges | Estimated payoff time without new charges | Estimated payoff interest | Modeled interest plus annual fees over payoff | Payoff time at comparison payment | Months saved at comparison payment |
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How to use Credit Card Interest Calculator
- Enter the current balance, APR, monthly payment, and any continuing new charges or fees.
- Enter a comparison payment to see the time difference.
- Use the payoff staircase to see how the balance path changes when the payment changes.
Calculator guide
Understanding Credit Card Interest Calculator
Credit-card interest is a month-by-month payoff problem: APR becomes a monthly rate, interest consumes part of each payment, and a larger payment can shorten both time and interest.
Calculation method
How the calculation works
Apply the APR as a monthly rate, disclose the first statement-cycle effect, and model payoff time and interest for two fixed-payment choices. Convert APR to a monthly rate, calculate first-month interest, then use fixed-payment amortization to estimate payoff months and total interest for the planned and comparison payments.
Detailed calculation process
Model fixed-payment credit-card payoff time and interest
The default uses a $6,800 balance, 24.99% APR, $275 monthly payment, no new charges or monthly fees, a $95 annual fee, and a $400 comparison payment.
General formula: j = APR/12I_1 = B APR/1200R_1 = P-I_1-C-Fn = ceil(-ln(1-(APR/1200)B/P)/ln(1+APR/1200))I_p = Pn-BK = I_p+A n/12n_c = payoff(B,APR,P_c)M = max(n-n_c,0) APR is divided by 12 for the periodic rate. The first month shows how interest, new charges, and fees affect principal reduction. The payoff formulas assume a fixed monthly payment and no new charges.
What each symbol means
Worked substitution with the default inputs
The default payoff estimate is 36 months, $3,100 of modeled interest, and $3,385 of interest plus prorated annual fees.
Purpose-built visual
Fixed-payment payoff staircase
The diagram compares planned and comparison payoff lanes with monthly balance steps, interest, and months saved.
Worked situations
Practical examples
- The default uses a $6,800 balance, 24.99% APR, $275 monthly payment, no new charges or monthly fees, a $95 annual fee, and a $400 comparison payment.
- The default payoff estimate is 36 months, $3,100 of modeled interest, and $3,385 of interest plus prorated annual fees.
Better inputs
Useful tips
- Use the purchase APR that applies to the modeled balance and do not substitute a cash-advance or penalty rate.
- Match payment timing and compounding assumptions to the statement cycle because daily balance methods can differ from a monthly estimate.
- Exclude new purchases and fees unless entered explicitly, then compare total payments with principal plus modeled interest.
Before relying on the result
Limitations and common mistakes
- Daily balance methods, statement timing, grace periods, promotional rates, variable APRs, issuer fees, new purchases, and payment allocation rules can change actual interest.
- The payoff calculation assumes fixed monthly payments and no new charges.
- If a payment is too low to amortize the balance, the model cannot represent a practical payoff.
Reference
Key terms
- Monthly periodic rate
- APR divided by 12 for the simplified monthly model.
- First-month interest
- Opening balance multiplied by the monthly rate.
- Payoff months
- Whole months required by the fixed-payment amortization formula.
Important note
Calculated from the entered values and stated financial terms. It is not a product quote, lending decision, tax filing, or investment recommendation.
Frequently asked questions
Why does the first payment not reduce the balance by the full payment?
Interest is charged first, so only the remaining payment reduces principal.
Why are payoff months rounded up?
The final payoff still requires part of a month, so the model counts a whole final payment cycle.
Does it include new charges?
The first-month reduction includes new monthly charges, but the fixed payoff estimate is the no-new-charge payoff reference.
Why include the annual fee?
It shows a broader modeled card cost during the payoff period.