How to calculate daily credit card interest

How to calculate daily credit card interest starts in the agreement, not in a slogan. In the United States, Truth in Lending, through Regulation Z, requires a credit-card issuer to disclose the annual percentage rate and the method used to compute the balance on which interest is charged. Many agreements then do the arithmetic daily. They state a daily periodic rate, often the APR divided by 365, and multiply it by each day’s balance or by an average daily balance across the cycle. The monthly statement is where those daily amounts are added up. “How is credit card interest charged monthly” usually means that sum, not a single multiplication done on the due date.

The payoff calculator on this site does something simpler, on purpose. It charges interest once a month at APR divided by 12, rounded to the cent, and then applies the payment. Snowball and avalanche can be compared only if they share a clock. A servicer’s daily subroutine is a different clock. The statement’s interest charge is what you were billed. The monthly model is the comparison.

Other countries, including the Indian card products people ask about by bank name, use their own statutes and their own day-counts. This page does not calculate HDFC, SBI, or any other named foreign card. If the contract says the rate is divided by 365, or by 12, or by something else, the contract is the calculation.

A monthly estimate and a daily rate

Take a $4,500 balance at a 24.99 percent APR, and hold the balance still so the only difference is the calendar. One month of interest at APR divided by 12 is 4,500 × 0.2499 ÷ 12 = $93.71. A daily rate of 24.99 percent divided by 365 is about $3.08 on that same balance. Thirty days of that rate is about $92.43. Thirty-one days is about $95.51. Twenty-eight days is about $86.27. February is not one-twelfth of the year, and a 31-day month is more than one-twelfth. The two methods are close. They are not the same bill, and the gap repeats every cycle you revolve.

interest = balance × (APR ÷ 12)

Balance $ APR %

Monthly estimate: $93.71

That widget is the monthly estimate only. It will not grow and shrink with the days in the month, and it will not see a payment that posts on the 12th. An average daily balance will. If you owe $4,500 for 20 days and $3,000 for the other 10 days of a 30-day cycle, the average is not $4,500 and it is not $3,000. A model that looks at one balance once a month cannot reproduce that path.

daily interest = balance × (APR ÷ 365) · monthly estimate = balance × (APR ÷ 12)

Balance held still $ APR % Days in the cycle

One day

$3.08

This many days

$92.40

APR ÷ 12

$93.71

Each day’s interest is rounded to the cent, then multiplied by the days. A card that uses a different divisor, or an average daily balance that moves, will not match. Nothing you type is sent.

The second widget holds the balance still and compares one day’s interest at APR divided by 365 with that many days, and with APR divided by 12. Use it to see the gap the example above named. Use the credit card payoff calculator when the question is a payment that hits a date. That calculator stays on the monthly clock so it can share a month with snowball and avalanche.

What the statement is allowed to mean

Regulation Z distinguishes methods. An average daily balance that includes new purchases is not an average daily balance that excludes them. A previous-balance method is a third thing. The disclosure on the account-opening papers and on the periodic statement is there so you can see which one you have. A blog that says “all cards use the average daily balance” is smoothing over a choice the regulation treats as meaningful.

A grace period, when the contract gives one on purchases, is the window in which purchase interest is not charged if you pay the statement balance in full by the due date. Cash advances are often excluded. The grace period usually disappears when you revolve. Carrying a promotional balance can also knock out the grace period on new purchases, which is a separate cost from the rate on the transferred amount. The statement date and the due date are the two days that bracket that window. They are not the day interest is “turned on” in a daily method. In a daily method, interest on a revolving balance is accruing through the cycle. The statement is the bill for that accrual.

Penalty APRs and promotional rates sit outside a flat monthly model. A teaser that is about to step up is a different APR from the one printed next to purchases. Sorting a payoff by the teaser aims extra money at the wrong balance. The comparison charts on this site use the monthly model so two orders share a clock. They are not a servicer’s interest subroutine, and they are not a promise that your statement will match the chart to the cent.

Where a payment goes when two rates share a card

If one balance on a card is at a promotional rate and another is at the purchase rate, extra money above the minimum is allocated by rule, not by preference. Regulation Z, at 12 C.F.R. § 1026.53, generally requires the creditor to apply the amount above the minimum to the higher-APR balance first. That can leave a transferred balance sitting at the low rate while your extra dollars attack the expensive one. It can also surprise someone who wanted the promo balance gone. The minimum itself can be applied differently. Read the allocation on the statement rather than assuming the whole payment hit the balance you named.

Using the monthly model without pretending it is the bill

The debt snowball and avalanche note uses the $93.71 figure on this same $4,500 balance so the orders can be ranked. If your agreement is daily, the dollar of interest in month one will not be $93.71, and a 31-day cycle will not match a 28-day cycle. The ranking can still be informative: a dollar of principal retired at 24.99 percent avoids more future interest than a dollar retired at 12.99 percent, under either a monthly or a daily application of those rates, as long as both debts use the same kind of calendar. What fails is copying the chart onto the statement and calling the difference an error.

If the question is the fee and the end date on a transferred balance, that cost is in what a balance transfer costs. Interest on the leftover balance after the promotion is a rate event. The fee on the day of the transfer is principal you did not owe the day before. They add. They are not the same line.

Interest that shows up after you pay the statement

A daily method keeps charging until the balance the agreement cares about is zero. If you have been revolving and then pay the statement balance in full, a few days of interest may already have accrued between the statement date and the day the payment posts. That charge often appears on the next statement. People call it residual or trailing interest. It is not a new APR. It is the same daily rate, applied to the days the balance was still there. Paying the next statement’s interest charge as well is what brings the balance to zero and, on many agreements, lets a purchase grace period start again. Paying only the old statement balance can leave that small charge to revolve, which is enough to keep the grace period off.

The monthly estimate used for payoff comparisons does not print this line. It applies one interest figure and then the payment inside the same modeled month. Use it to rank snowball against avalanche. Use the statement, including the following cycle, to see what the issuer actually charged. If those two disagree, the statement is the bill. The model is the shared clock, and it will stay a shared clock even when a 31-day cycle and a trailing-interest line make the first month look different.