Credit Card Interest Calculator
Estimate interest for a day count with a simple daily rate. Optional monthly payment can sketch months to pay off. Informational, not lending advice. Issuer methods vary.
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How to estimate card interest
- Enter the balance you want to test.
- Enter the card APR and the number of days in the period.
- Read interest ≈ balance × (APR/100/365) × days.
- Optional: enter a monthly payment to sketch months to clear the balance.
- Issuer average-daily-balance rules can differ. Not lending advice.
Credit card interest sketch
Daily rate × days × balance
| Daily rate | APR/100/365 |
|---|---|
| Interest | Balance × daily rate × days |
| Days range | 1 to 365 |
| Optional payoff | Revolving amortization if payment > 0 |
| Grace period | Not modeled |
| Advice | Informational. Not lending advice. |
What this card interest page estimates
Many teaching examples treat card interest as balance times a daily rate times days. This page uses that simple product. Real statements may use average daily balance, grace periods, or tiered APRs.
Interest formula
Daily rate = APR/100/365. Interest for the period = balance × daily rate × days. If you enter a monthly payment greater than zero, the engine also attempts a revolving payoff sketch with that payment.
Related pages
Full payoff planning: credit card payoff and debt payoff. Consolidation check: debt consolidation.
Use cases
Rough cost of carrying a balance for a billing cycle. Comparing APRs on the same balance and day count. Seeing whether a payment clears interest.
Worked example
$3,000 at 22.9% APR for 30 days. Daily rate = 0.229/365. Interest ≈ 3000 × daily rate × 30. That is the default sketch before any optional payment.
Limits
No grace period, no cash-advance APR split, no fees. Informational, not lending advice. See the disclaimer.