Credit Card Interest Calculator
See exactly how much interest a credit card balance accrues over time.
Your Details
Principal vs. Interest
What you'll actually pay in total
- Principal$3.0K
- Interest$819.8
Payoff Time by Monthly Payment
How faster payments shorten your timeline
Balance Over Time
How your balance declines as you pay it down
Principal vs. Interest by Year
How much of each year's payments go to interest
How It Works
- Enter your current balance and interest rate.
- Enter the amount you plan to pay each month.
- Press Calculate to see your payoff timeline.
Formula Used
Each month's interest is charged on the remaining balance, then the rest of the payment reduces principal.
Good to Know
- • Extra payments go straight to principal.
- • Higher-APR balances cost more the longer they carry.
Important Notes
- • Assumes a fixed payment and fixed rate.
- • If payment doesn't cover interest, balance won't shrink.
How Card Issuers Calculate Interest
Most credit cards charge interest based on your average daily balance across the billing cycle, applying roughly APR ÷ 365 each day. This calculator simplifies that to a standard monthly charge of APR ÷ 12 on the balance at the start of each month, which is a close approximation for balances that don't change dramatically mid-cycle.
Grace Periods Can Avoid Interest Entirely
Many cards offer a grace period — if you pay your statement balance in full by the due date, new purchases may accrue no interest at all. That grace period typically disappears once a balance is carried month to month, which is when the interest math modeled here starts to apply.
Clarifying the Terms
- Average daily balance — the method most issuers use to calculate monthly interest, based on the balance each day of the cycle.
- Daily periodic rate — APR divided by 365, applied to the balance each day.
Testing It With an Example: One Month's Interest Charge
On a $3,000 balance at 23% APR, held for a full 30-day billing cycle:
Monthly interest ≈ $3,000 × 0.063% × 30 ≈ $56.71
Paying even a portion of the balance mid-cycle lowers the average daily balance for the remaining days, which is why paying earlier in the billing cycle — not just by the due date — can shave a small amount off the interest charged that month.
Balance Level Comparison Table
At 23% APR, one month's interest:
| Balance | Monthly Interest |
|---|---|
| $1,500 | $28.75 |
| $3,000 | $57.50 |
| $6,000 | $115.00 |
Things Often Overlooked About Card Interest
- Not using the grace period — paying the full statement balance avoids interest on new purchases entirely.
- Only paying near the due date — paying earlier in the cycle can lower the average daily balance.