Total Interest
Total Payments
Total Paid
Table of Contents
Now that you know how much your paying, what's next?
When will my credit card be fully paid off?How credit card interest is actually calculated
Credit card interest is calculated daily on your average daily balance — not once a month, not on your statement balance. The math:
Daily interest = (APR ÷ 365) × Daily balance
Monthly interest = sum of daily interest for the billing cycle
This is why two cards with the same APR can produce different interest charges depending on when transactions happen during the cycle, when you pay, and what balance you carry day to day.
Worked example using the calculator's defaults ($1,200 balance, 16% APR, $50/month payment):
- Daily rate = 16% ÷ 365 = 0.0438%
- Monthly interest (first month, assuming flat balance): $1,200 × (0.16/12) = $16
- Of the $50 payment: $16 covers interest, $34 reduces principal
- Time to pay off entirely: approximately 29 months
- Total paid: about $1,450; total interest: about $250
For a $1,200 balance at $50/month, you spend 2.5 years repaying and lose 17% of the original balance to interest. At higher APRs and lower payment ratios, the multiplier gets much worse — see the next section.
APR, daily rate, effective rate — what's the difference?
Credit card interest involves three different rates that often get conflated:
- APR (Annual Percentage Rate). The headline number you see on disclosures (e.g., 21.99%). This is the nominal annual rate.
- Daily periodic rate. APR ÷ 365. The actual rate applied to your balance each day. A 21.99% APR has a daily rate of 0.0603%.
- Effective annual rate (EAR). What 365 days of daily compounding actually produces. (1 + daily rate)365 − 1. The 21.99% APR card has an effective rate of about 24.6% — meaningfully higher than the stated APR.
This is why credit card balances grow faster than people expect: the disclosed APR understates the actual compounding behavior. The effective rate is what determines how fast unpaid balances grow if you only make minimum payments.
Multiple APRs on the same card
A single credit card typically has several different APRs, each applying to a different type of transaction:
| APR type | Typical rate | When it applies |
|---|---|---|
| Purchase APR | 18–30% | Normal purchases (after grace period if balance carried) |
| Cash advance APR | 22–36% | ATM withdrawals, casino chips, money orders. NO grace period. |
| Balance transfer APR | Often 0% promo, then 18–25% | Balances moved from another card. Promo rates have specific durations. |
| Penalty APR | Up to 29.99% | Triggered by late payment. Can apply for 6 months minimum. |
| Introductory APR | Often 0% for 12–18 months | New purchases on a new card. Reverts to standard purchase APR after promo. |
If you're carrying a balance with multiple APRs (say, a purchase balance and a cash advance balance), federal CARD Act rules require payments above the minimum to go toward the highest-APR balance first — but the minimum payment can still be applied to whichever balance the issuer chooses.
The grace period: how to avoid interest entirely
Almost all US credit cards offer a grace period between your statement closing date and your payment due date — typically 21–25 days. During this period, if you pay your statement balance in full, you owe NO interest on the purchases from that cycle.
The trap: the grace period only applies if your previous statement was also paid in full. As soon as you carry a balance from one month to the next, the grace period disappears — meaning interest starts accruing from the transaction date on EVERY new purchase, not just on the carried-over balance.
This is why "I'll pay it off later" with credit cards is much more expensive than people realize. The moment a balance carries forward, all new purchases also start accruing interest immediately. To restore the grace period, you typically need to pay the full statement balance for two consecutive cycles.
Beyond interest: the other fees
- Annual fee: $0 to $700+ depending on card. Premium cards charge fees but offer rewards/perks that can offset them for heavy users.
- Late payment fee: $25–$41 (capped by CARD Act). Triggers penalty APR on many cards.
- Cash advance fee: $10 or 3–5% of advance, whichever is higher. Plus immediate-accruing interest at the cash advance APR.
- Foreign transaction fee: 0–3% on purchases in foreign currency. Some travel-focused cards waive this.
- Returned payment fee: $25–$41 if a payment bounces.
- Over-limit fee: Now requires opt-in under CARD Act; most issuers no longer offer the option.
How credit card issuers make money
Understanding the business model helps you avoid being its product:
- Interest on revolving balances (the biggest profit source). Industry research suggests about half of US cardholders carry a balance, generating tens of billions in interest annually.
- Interchange fees charged to merchants on every transaction (typically 1.5–3% of the transaction). This is why "rewards" cards are sustainable — the issuer is sharing some of the merchant fee with you as cashback.
- Annual fees on premium cards.
- Late and penalty fees.
The most profitable customers from the issuer's perspective are not the ones who pay in full and earn rewards — they're the ones who carry balances and pay interest. If you can stay in the first group, credit cards become a profitable tool for you (rewards + free 21-day float on every purchase). If you slip into the second, the math flips.
Sources & references
- Consumer Financial Protection Bureau — Credit Cards — CFPB consumer guidance and rules under the CARD Act.
- Federal Reserve G.19 — Consumer Credit — current average US credit card interest rates and outstanding consumer credit.
- CFPB Consumer Credit Card Market Report — biennial industry analysis covering fees, rates, and consumer behavior.
FAQs
Two reasons. First, credit cards are unsecured — there's no collateral the issuer can repossess if you stop paying. Second, default rates on revolving credit are much higher than on installment loans. To stay profitable across all customers including the ones who don't pay, issuers charge rates (typically 18–30%) that exceed the cost of secured borrowing. The math works out for them; it works against you whenever you carry a balance.
APR (Annual Percentage Rate) is the annualized rate. The daily periodic rate is APR divided by 365. Most US credit cards charge interest daily on your average daily balance — so a 22% APR card actually accrues at 22%/365 = 0.0603% per day. Over a year of carrying a $1,000 balance, this compounds to slightly more than 22%, because daily compounding produces a higher effective rate than simple annual interest.
Pay your statement balance in full each month before the due date. Almost all US credit cards offer a grace period (typically 21–25 days from statement to due date) during which no interest accrues on new purchases — but only if your previous statement was paid in full. Once you carry any balance, the grace period typically vanishes and interest accrues from the date of each new transaction.
- Purchase APR applies to normal purchases — typically 18–30% on most cards.
- Cash advance APR applies when you use the card as cash (ATM withdrawals, casino chips). Usually 5–10% higher than purchase APR, AND there's no grace period — interest accrues immediately. Plus a cash advance fee (typically 3–5%) on the withdrawal itself.
- Penalty APR kicks in if you miss a payment or violate card terms. Often 29.99% (the maximum many issuers can charge) and can apply for 6 months minimum.
Two common reasons. First, daily compounding produces a slightly higher effective annual rate than the stated APR (a 22% APR works out to about 24.6% effective annually with daily compounding). Second, if you make a purchase and don't pay in full, you lose the grace period — interest accrues retroactively from the transaction date on the WHOLE balance, including new purchases. The result is more interest than you'd expect from looking at just your average balance.