Credit card interest calculator

Enter a balance and the rate on your statement. See the interest per day, per billing cycle and per month, and what the balance grows to if you carry it.

Calculated in your browser
Formula and rounding
Reviewed October 9, 2026

Your numbers

Currency

Card balance

Your statement balance, or the balance at the start of the cycle

Interest rate

A simple annual rate, as quoted on US, Canadian and Australian cards

How the rate is quoted

Nominal APREffective APRMonthly rate

Days in the issuer’s year

365 days360 days

Most issuers divide the APR by 365; some use 360

Billing cycle length

30 days30.4167 days (365 ÷ 12)

Months the balance is carried

For the carried-over table: nothing paid, interest left to compound (1–60)

Interest this monthExample

$40.00

$1.32 a day · $39.45 per 30-day cycle · $480.00 a year with the balance held flat

Starting balance$2,000.0079%
Interest after 12 months unpaid$536.5021%

Per day: $1.32on the starting balance
Per billing cycle: $39.4530-day cycle
Per year, balance held flat: $480.00interest paid each month
Daily periodic rate: 0.06575%APR ÷ 365
Monthly rate: 2.0000%
Effective annual rate: 26.82%if interest compounds unpaid

Balance with interest compounding

Left unpaid for 12 months, the balance grows to $2,536.50, adding $536.50 of interest.

Assumptions

Rate 24% is a nominal APR: monthly rate = APR ÷ 12, daily rate = APR ÷ 365.
Cycle interest uses the average daily balance over 30 days; days with a credit balance count as zero (Reg Z §1026.14(d)).
No grace period is applied: if you pay the statement balance in full by the due date, most cards charge no interest on purchases.
Monthly figures hold the balance flat; the carried table lets interest compound unpaid with no new spending or fees.
Issuers differ (day-count, posting dates, rounding), so your statement can differ by a few units.

This calculator needs JavaScript to recalculate. The figures shown are a worked example; the method is explained below and on the methodology page.

Your numbers stay in your browser. Nothing you type is sent to our servers. More on privacy

Estimates for general information only — not financial, credit or legal advice. Your actual figures depend on your lender’s or card issuer’s exact terms, fees, minimum-payment rules, interest calculation method and any changes they make. Check your statements and speak to a qualified adviser before making decisions. Issuers work out interest on daily balances with their own day count, posting dates and rounding, so the interest on your statement can differ from these figures. Disclaimer · Report an error

How to use it

How to calculate how much interest you will pay on your credit card

Credit card interest is quoted as a yearly rate but charged in much smaller slices: most issuers turn the APR into a daily rate, apply it to the balance for each day of the billing cycle, and add the total to the next statement. That is why a balance of 2,000 at 24% does not simply cost 480 in a year. It costs roughly 1.32 a day, about 40 a month, and more than 480 over a year if the interest is left on the card to compound.

This calculator takes a balance and the rate on your statement in whichever form your issuer quotes it, works out the daily, monthly and effective annual rates, and shows the interest per day, per cycle and per month. Switch on average-daily-balance mode to add purchases and payments by day, and the cycle’s interest is calculated the way issuers describe it in their agreements. The carried-over table shows what happens to the balance if nothing is paid for a number of months.

1
Enter the balance and the rate
Type the balance from your statement and the interest rate, then say how it is quoted: a nominal APR (United States, Canada, Australia), an effective APR (United Kingdom, Ireland) or a monthly rate. The calculator converts between all three.
2
Check the day count and cycle length
Most issuers divide the APR by 365 to get the daily periodic rate; some use 360. The billing cycle is typically around 30 days, and 30.4167 (365 ÷ 12) is the average month. Both choices are on the form and your card agreement states which apply.
3
Read the interest and the carried-over table
The headline shows this month’s interest, with the per-day, per-cycle and per-year figures beside it. Set the number of months carried to see the balance grow with nothing paid, month by month, and export the table as CSV.

What this calculator does

Interest per day, per billing cycle, per month and per year from one balance and rate
Accepts a nominal APR, an effective APR or a UK-style monthly rate, and shows all three
Daily periodic rate on a 365- or 360-day year, with a 30- or 30.4167-day cycle
Average daily balance mode: add purchases and payments by day for the cycle’s interest
Carried-over table and chart of the balance growing month by month if nothing is paid
Every step of the working shown, with the assumptions behind it, plus CSV export
Any currency; nothing you type leaves your browser

Worked example

Worked example: 2,000 at 24% APR

Daily, monthly and yearly interest on one balance

You owe 2,000 (any currency) on a card with a nominal APR of 24%, the issuer uses a 365-day year, and the billing cycle is 30 days. The daily periodic rate is 24% ÷ 365 = 0.065753% and the monthly rate is 24% ÷ 12 = 2%.

Figure	Amount	How
Interest per day	1.32	2,000 × 0.065753%
Interest per 30-day cycle	39.45	2,000 × 0.065753% × 30
Interest per month	40.00	2,000 × 2%
Per year, balance held flat	480.00	2,000 × 24%
Effective annual rate	26.82%	(1 + 2%)¹² − 1
Per year, interest left to compound	536.48	2,000 × 26.82%

The 30-day cycle and the calendar month give slightly different answers, 39.45 against 40.00, because 30 days is a little less than a twelfth of a year. On a 30.4167-day cycle the two agree at 40.00, and on a 360-day year the daily rate rises to 0.066667%, so a 30-day cycle costs exactly 40.00 and a day costs 1.33.

Carrying the balance. If nothing is paid, each month’s interest is added to the balance and attracts interest itself. In month 1 the interest is 40.00 and the balance becomes 2,040.00; in month 2 it is 40.80 and the balance 2,080.80; by month 6 the interest is 44.16 on a balance of 2,252.33; and after 12 months the balance is 2,536.50, having added 536.50 of interest. Carry it for 24 months and the interest reaches 1,216.90, with the balance at 3,216.90.

Average daily balance. Suppose the cycle starts at 2,000, you buy something for 400 on day 8 and pay 500 on day 20. The balance is 2,000 for days 1–7, 2,400 for days 8–19 and 1,900 for days 20–30, so the average daily balance is 2,123.33 and the cycle’s interest is 2,123.33 × 0.065753% × 30 = 41.88, rather than the 39.45 on the starting balance alone.

A UK-style monthly rate. Enter 1.9% a month instead and the calculator reports an effective APR of 25.34% and a nominal-equivalent rate of 22.80%. The same 2,000 then costs 38.00 a month, 1.25 a day, and 506.80 if carried unpaid for 12 months. Enter a UK effective APR of 24.9% and the monthly rate is 1.8701%, the first month’s interest 37.40, and 12 months unpaid adds 497.99.

The method

How it’s calculated

The calculator first puts the rate you enter into one form, the monthly periodic rate i:

Nominal APR (US, Canada, Australia, New Zealand): i = APR ÷ 12.
Effective APR (UK, Ireland): i = (1 + APR)^1/12 − 1, the monthly rate that compounds to the quoted annual figure.
Monthly rate: used as entered.

From i it derives the nominal APR 12 × i, the effective annual rate (1 + i)¹² − 1, and the daily periodic rate DPR = nominal APR ÷ day count, where the day count is 365 or 360. Each money figure is then a single multiplication rounded half-up to the smallest unit of the currency:

interest per day = round(balance × DPR)
interest per cycle = round(average daily balance × DPR × cycle days)
interest per month = round(balance × i)
per year, balance held flat = round(balance × nominal APR)
per year, interest compounding = round(balance × effective annual rate)

Without transactions the average daily balance is simply the balance you entered. With transactions, the calculator walks through the cycle one day at a time, adds each purchase or payment on its day, counts any day with a credit balance as zero, and divides the total by the number of days, the average daily balance method that Regulation Z §1026.14(d) refers to. The cycle is rounded to whole days in this mode.

The carried-over table repeats one step for each month: interest = round(balance × i), then balance = balance + interest. Because each month is rounded separately, the 12-month total in the table (536.50 in the example) can differ by a few units from the single-rounding yearly figure (536.48). The same monthly step, with payments taken off, is what the credit card payoff calculator and the credit card minimum payment calculator use, so figures across the three tools agree.

Full method, rounding and tests on the methodology page

From APR to the daily rate: how issuers actually charge interest

The APR on a card agreement is a yearly figure, but the interest on a statement is worked out from a daily periodic rate. In the United States the periodic rate is defined in Regulation Z §1026.14 as the rate of finance charge per unit of time, and the CFPB notes that many issuers work out interest daily from the average daily balance. The daily periodic rate is the APR divided by the days in the issuer’s year, 365 for most cards and 360 for a few, and it is multiplied by the balance on each day of the billing cycle. A 24% APR is therefore 0.065753% a day on a 365-day year and 0.066667% on a 360-day year, a difference of about 1.4% in the interest charged.

Because the daily rate is applied to each day’s balance, the figure that matters is the average daily balance: the sum of the balance at the end of each day in the cycle divided by the number of days. A purchase early in the cycle raises the average more than the same purchase near the end; a payment made early lowers it. Some agreements compound daily, adding each day’s interest to the balance before the next day’s calculation, which increases the cost slightly. This calculator applies simple daily interest within the cycle and compounds monthly in the carried-over table, which is the usual simplification and matches most statements to within a few units.

The grace period is the reason many people never pay card interest at all. In the US and most other markets, if you pay the statement balance in full by the due date, no interest is charged on the purchases in that cycle. The grace period normally covers purchases only, and only when the previous statement was also paid in full; cash advances and balance transfers usually accrue interest from the day of the transaction. Once a balance is carried, the grace period on new purchases is lost until the card is paid in full again, so interest starts from the purchase date. The figures on this page assume the balance is carried, with no grace period. Our guide to how credit card interest works walks through a full statement cycle with dates.

Monthly rates, effective APRs and the UK convention

UK card statements usually show a monthly rate such as 1.9% alongside an APR, and the APR is the compounded, effective annual figure rather than twelve times the monthly rate. Under the FCA’s total charge for credit rules (CONC App 1.2), the APR for a credit card is calculated from the actual charges and timing of repayments and expressed to at least one decimal place, rounded up when the next digit is 5 or more. Twelve times 1.9% is 22.8%, but 1.9% a month compounded for a year is 25.34%, and it is the second figure that appears as the APR on a UK statement. US-style quoting works the other way round: the APR is twelve times the monthly rate, and the true annual cost of carrying a balance, 26.82% on a 24% APR, is higher than the headline figure.

This is why the calculator asks how the rate is quoted. Select “monthly rate” and enter the figure from a UK statement, or “effective APR” and enter the headline APR, and the daily, monthly and annual figures are all derived from the same monthly rate. Select “nominal APR” for a US, Canadian, Australian or New Zealand card. In every case the stats panel shows all three rates, so you can compare a card quoted one way against a card quoted the other. The rate on a representative-APR advertisement is not necessarily the rate on your account; use the rate from your own statement or agreement.

Note that a UK representative APR for a card also has to include any annual fee, so it can be higher than the rate implied by the monthly interest alone. If you want to test what a balance costs under a different rate or after a promotional period ends, change the rate and compare. To see how long a balance takes to clear at a given payment, the credit card payoff calculator continues from the same monthly rate, and the debt payoff calculator handles several cards and loans together.

Limits

Good to know

Issuers differ in day count (365 or 360), in whether the daily interest compounds within the cycle, in the day on which transactions post, and in rounding. The interest on your statement can differ from these figures by a small amount; the statement is the authoritative figure for your account.
Cash advances, balance transfers and purchases often carry different rates on the same card, and promotional 0% periods change the first months entirely. Enter the rate that applies to the balance you are looking at.
The carried-over table assumes nothing is paid and nothing new is spent. Any payment, fee or purchase changes the balance and the path; use the credit card payoff calculator for a schedule with payments, and the guide to credit card minimum payments explains how issuers set the minimum.
Paying the statement balance in full by the due date normally means no interest on purchases at all. If you pay part of the balance, interest is usually charged on the whole balance from the transaction dates, not just on the part left unpaid.
Rates are quoted differently in different countries, and the calculator converts between them as arithmetic only. It does not say which card is better value; the guides on this site explain the conventions and leave the decision to you.

Privacy

What happens to the numbers you type

Your numbers stay in your browser. DebtWren works out your results on your device. We don’t send the balances, rates or payments you type to our servers or store them. If you allow analytics, we record only broad ranges (for example “£2,000–£5,000 of debt”) to understand how the calculators are used. Like any website with ads, this page also loads advertising scripts; see our Privacy Policy.

The calculator is plain code running in this tab. It makes no network requests with your figures, and nothing is saved when you leave unless you choose to keep it. Read the privacy policy for how ads and analytics work on this site.

Keep going

Related calculators and guides

FAQ

Questions people ask

How is credit card interest calculated?

Most issuers divide the APR by 365 to get a daily periodic rate, multiply it by the balance on each day of the billing cycle, and add the total to the statement. On 2,000 at 24% APR that is 0.065753% a day, or about 1.32 a day and 39.45 over a 30-day cycle. The calculator shows each of these steps and the rates behind them.

How much interest will I pay on my credit card per month?

As a close approximation, multiply the balance by the APR and divide by 12: 2,000 × 24% ÷ 12 = 40.00 a month. The exact charge on a statement uses the daily rate and the average daily balance over the cycle, so it will be a little lower on a 30-day cycle (39.45) and higher after a cycle with purchases early in it.

What is the daily periodic rate?

The APR divided by the number of days in the issuer’s year, usually 365. It is the rate applied to the balance each day. A 24% APR gives a daily periodic rate of 0.065753% on a 365-day year and 0.066667% on a 360-day year. The calculator shows it to five decimal places because the difference matters over a full cycle.

What is the average daily balance and why does it matter?

It is the sum of the balance at the end of each day in the billing cycle divided by the number of days (Regulation Z §1026.14(d)). Issuers charge interest on this average, so a purchase early in the cycle costs more interest than the same purchase near the end, and an early payment saves more. Switch on average-daily-balance mode and add transactions by day to see the effect.

Why is the effective annual rate higher than the APR?

A US-style nominal APR is twelve times the monthly rate. If interest is left on the card it compounds, so the real yearly cost is 1 plus the monthly rate, raised to the power of 12, minus 1: 26.82% for a 24% APR. UK and Irish cards quote the APR the other way, as the compounded figure, which is why a UK monthly rate of 1.9% appears as a 25.34% APR rather than 22.8%.

Do I pay interest if I pay my credit card in full every month?

Usually not on purchases. Most cards give a grace period between the statement date and the due date, and paying the full statement balance by then means no interest on that cycle’s purchases. Cash advances generally accrue interest from the transaction date, and once you carry a balance the grace period on new purchases is lost until the card is paid in full again.

How do I convert a monthly interest rate to an APR?

For the compounded (UK-style) APR, add 1 to the monthly rate, raise to the power of 12 and subtract 1: 1.9% a month gives 25.34%. For a US-style nominal APR, multiply by 12: 22.8%. Select “monthly rate” in the calculator and both figures appear in the stats panel.

Does a 365-day or 360-day year make a difference?

Slightly. Dividing a 24% APR by 360 rather than 365 raises the daily rate from 0.065753% to 0.066667%, so a 30-day cycle on 2,000 costs 40.00 instead of 39.45. Over a year the 360-day convention charges about 1.4% more interest. Your card agreement states which day count the issuer uses.

Sources

Sources and review

Page reviewed October 9, 2026 by the DebtWren team · Methodology · Changelog · Report an error