Credit Card Interest Calculator

Find out exactly what your balance is costing you. See your next finance charge, how long it will take to pay off, and how much interest you'll really pay — all in one place.

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How credit card interest is actually calculated

Credit card interest looks mysterious on a statement, but the math is straightforward. Issuers use four inputs: your average daily balance, your APR, the number of days in the billing cycle, and whether your grace period applies. Each one moves the final number — sometimes by a lot.

  • Grace period. If you paid your previous statement in full by the due date, your card's grace period waives interest on new purchases — your finance charge is $0. The moment you carry a balance from one cycle to the next, the grace period disappears and interest starts accruing on every new purchase from the day it posts.
  • Average daily balance. Issuers add up your balance at the end of every day in the billing cycle and divide by the number of days. Pay early in the cycle and the ADB drops, lowering your interest. Wait until the due date and the ADB stays high.
  • APR. Your annualized rate, divided by 365 to get the daily periodic rate. A 19.99% APR translates to roughly 0.0548% per day — small until it compounds across thousands of dollars and hundreds of days.
  • Days in the billing cycle. Usually 28–31. The longer the cycle, the more days interest accrues.

Put it together and the formula is just: ADB × (APR ÷ 365) × days. That's it. The calculator above does this for you, plus projects what happens month after month if you're carrying a balance.

Worked example

Your average daily balance for the cycle is $2,000, your APR is 19.99%, and the cycle has 30 days. The daily periodic rate is 19.99 ÷ 365 ≈ 0.0548%. Multiply through: $2,000 × 0.000548 × 30 ≈ $32.86. That's the finance charge that would land on your next statement.

The minimum payment trap

If credit cards have a single most expensive feature, it's the minimum payment. It looks reasonable on a statement — a small, manageable number — but the math behind it is built to keep balances on the books for as long as possible.

What's actually in a minimum payment

Most issuers calculate the minimum as a small percentage of your balance — typically 1% to 3% — with a floor of around $10 to $30. Some cards add that month's interest and any fees on top, which is honest but barely changes the dynamic. A few cards (Capital One Canada is the most common example) skip the percentage entirely and use a flat minimum like $10. Either way, the payment is engineered to be small.

Why the math doesn't work in your favour

When you only pay the minimum, most of the payment goes straight back to the issuer as interest, and only a sliver chips away at the principal. As the balance shrinks, the percentage-based minimum shrinks with it — so the payment gets smaller every month, dragging the payoff out further. The effect compounds: smaller payments → less principal paid → more interest owed → smaller next payment. It's a treadmill, and it's deliberate.

A real $5,000 example

You owe $5,000 on a card with a 19.99% APR. Three scenarios, identical starting point:

  • Pay only the minimum (~2% of balance): Roughly 23+ years to pay off, and around $5,800 in total interest — more than the original balance.
  • Pay $200/month flat: About 32 months (under 3 years) and roughly $1,500 in interest. One small change — a fixed $200 instead of a declining 2% — saves over $4,000.
  • Pay $500/month: About 11 months and roughly $540 in interest. Doubling again from $200 cuts both the timeline and total interest by another two-thirds.

Plug your own numbers into the calculator above and watch the "Minimum only" line in the chart. The shape of that curve is the trap, visualised.

The disclosure box on your statement

Most Canadian and U.S. statements now include a regulator-mandated box that says, in plain language, "If you make only the minimum payment, you will pay off this balance in X years and pay $Y in interest." Read that box. If your statement doesn't include one, check the issuer's online portal — the figures are usually the most honest line of communication a credit card company will print on a piece of paper.

Quebec's 5% rule

In Quebec, provincial law has been steadily ratcheting the minimum payment up for newer accounts — toward 5% of the balance as of 2025. The intent is exactly the math you just saw: a higher floor on the minimum payment dramatically reduces the time consumers stay in debt. Other Canadian provinces and U.S. issuers are not bound by the same rule, but the lesson generalizes — pay more than the minimum.

What happens if you miss a minimum payment

Three things can happen, often in sequence: a late fee (typically up to $40 in Canada and up to $30–$40 in the U.S.), a hit to your credit score if the payment is more than 30 days late, and — at 60+ days late — a penalty APR that can push your rate to 29.99% or higher and stick around for at least six months. The cheapest minimum payment is the one you make on time, every time, even if you can only afford the floor.

How to actually pay less interest

The cheapest path is always the same: don't carry a balance. The grace period was designed exactly for this — pay in full, never pay a cent of interest. If you're already carrying a balance, here's what actually moves the needle, ordered roughly by impact.

  • Pay more than the minimum — even a little. Adding $50 or $100 a month to the minimum can knock years off the payoff and thousands off the total interest. The calculator above will tell you the exact numbers for your situation.
  • Pay multiple times per month. Because interest is calculated on the average daily balance, paying twice a month — once mid-cycle, once near the due date — pulls your ADB down faster than a single big payment on the due date.
  • Move the balance to a 0% intro APR card. A balance transfer card with 6–18 months at 0% can interrupt the interest entirely, letting every dollar of payment go to principal. Watch the transfer fee (usually 3–5%) and have a payoff plan before the promo expires — otherwise you just swap one APR for another.
  • Call and ask for a lower APR. If your account is in good standing and you've been a customer for a while, issuers can — and often do — drop the rate by 2–5 percentage points on request. It costs nothing to ask and the call is rarely longer than 10 minutes.
  • Consolidate with a personal loan or line of credit. Unsecured personal loans typically run 8–15% APR, line of credit rates are often even lower. Rolling a 19.99% card balance into a 10% loan can roughly halve the interest you pay over the payoff period.
  • Pick a payoff method and commit to it. Avalanche (highest APR first) saves the most money mathematically. Snowball (smallest balance first) saves the most motivation. Either beats paying minimums across multiple cards forever.

Your card has more than one APR

The number on the front of the card disclosure is the purchase APR — but most cards quietly run several rates in parallel. Knowing which one applies to which transaction is half the battle.

  • Purchase APR. The headline rate. Applies to everyday purchases, and the only one your grace period covers when you pay in full.
  • Cash advance APR. Withdrawing cash from an ATM with your credit card. Usually several points higher than the purchase APR, and the kicker: no grace period. Interest accrues from the moment the cash leaves the machine. Avoid unless absolutely necessary.
  • Balance transfer APR. What you pay on balances moved from another card. Often a promotional 0% for 6–18 months, then it reverts to the standard rate. The best 0% offers are how disciplined cardholders break out of the minimum-payment trap.
  • Penalty APR. Triggered if you're 60+ days late on a payment. Often 29.99% and applied to your entire balance. It's usually the single most expensive thing your card can do to you, and the trigger is missing one payment.
  • Promotional / introductory APR. Time-limited rates on new purchases or transfers. Set a calendar reminder for the day before they expire — that's the day to finalize your payoff plan, not the day after.

Smart ways to use this calculator

  • Compare payment scenarios. Switch to the Payoff plan tab and try doubling your monthly payment. The total interest often drops by more than half.
  • See the cost of paying only the minimum. The comparison view shows what happens if you pay roughly 2% of the balance — the most common reason debt outlives a decade.
  • Check your grace period. In the Monthly charge tab, toggle the grace-period switch to see what your finance charge would be if you paid last statement in full. The number you want to see is $0.
  • Share your scenario. Every input is stored in the URL — copy the link to send to a partner, advisor, or your future self.

Frequently asked questions

Most issuers use the average daily balance (ADB) method. They take the sum of your daily balances over the billing cycle, divide by the number of days to get the ADB, then multiply that by your daily periodic rate (APR ÷ 365) and the number of days in the cycle. So if your ADB is $2,000, your APR is 19.99%, and the cycle is 30 days: $2,000 × (0.1999 ÷ 365) × 30 ≈ $32.86 in interest.

A grace period is the window between the end of your billing cycle and your payment due date — usually 21 to 25 days — during which new purchases don't accrue interest, *if* you paid the previous statement balance in full. The moment you carry a balance from one cycle to the next, the grace period vanishes and new purchases start accruing interest from the day they post. Paying in full each month is the single most powerful thing you can do to avoid interest entirely.

Minimum payments are designed to be small — typically about 2% of your balance or $25, whichever is greater. At a 19.99% APR, most of your minimum payment goes toward interest, not principal, so the balance shrinks slowly. The longer the balance lingers, the more interest accrues. Use the comparison view in the calculator to see the difference: doubling the minimum payment often cuts payoff time and total interest by more than half.

The statement balance is the full amount you owe at the end of the billing cycle — paying it in full keeps you in the grace period and means you owe $0 in interest. The minimum payment is the smallest amount you can legally pay without being marked late; it's usually 1–3% of the statement balance with a small dollar floor. Paying the minimum keeps the account in good standing but does almost nothing to reduce the balance, and you lose the grace period the moment you don't pay in full.

Yes, and more often than people realize. If your account is in good standing — payments on time, decent credit score, ideally a year or more of history — call the number on the back of your card and ask if your APR can be reduced. Mention competing offers if you have any. Issuers can typically lower the rate by 2–5 percentage points on the spot. The worst they can say is no, and the call rarely takes more than 10 minutes. Re-ask every 6–12 months.

A balance transfer card lets you move existing debt to a new card with a 0% (or very low) promotional APR for 6–18 months. During that window every dollar of payment goes to principal, not interest — which is why this is the single most powerful interest-reduction tool for someone carrying a balance. Watch the transfer fee (typically 3–5% of the moved balance), and have a payoff plan that finishes before the promo expires. After the promo, the rate reverts to the card's standard APR, often a high one.

The math is the same, but the inputs differ. Cash advances usually have a higher APR and no grace period — interest starts accruing the day you take the advance. Balance transfers often have a 0% promotional APR for a set period, then revert to the standard rate. For balance transfers specifically, use our balance transfer calculator, which handles promotional rate windows correctly.

Three things, often in sequence. (1) A late fee, usually up to $40 in Canada and $30–40 in the U.S., added to your next statement. (2) A hit to your credit score if the payment is more than 30 days late and gets reported to the bureaus. (3) At 60+ days late, a penalty APR — often 29.99% or higher — that applies to your entire balance, and stays in place for at least six months. The cheapest minimum payment is the one you make on time, even if it's only the floor amount.

APR (Annual Percentage Rate) is the simple annualized rate that credit cards advertise. APY (Annual Percentage Yield) accounts for compounding within the year. Because credit card interest is compounded daily, your *effective* annual rate is slightly higher than your APR. For a 19.99% APR compounded daily, the effective rate is about 22.13%. The calculator uses the daily periodic rate so the math reflects what you'd actually be charged.

In Canada, standard purchase APRs range from about 19.99% on rewards cards to 12–13% on dedicated low-interest cards (RBC Visa Classic Low Rate, MBNA True Line, etc.). If you regularly carry a balance, the rewards on a 19.99% card are almost always wiped out by interest — switching to a low-rate card is usually the bigger win. A 'good' APR depends on your situation, but anything under 15% is competitive in the Canadian market.

Close, but not exact. We use the standard ADB method and assume a single APR with no fees, late charges, or promotional rates layered on. Your actual statement may use a slightly different ADB calculation (some issuers use two-cycle billing or include unpaid finance charges in the balance), and may include items we don't model. Treat the numbers as a strong estimate and a planning tool, not a billing dispute reference.