How Is Credit Card Interest Calculated? (2026 Guide)

The standard credit card interest formula

Almost every U.S. credit card uses the same three step formula, disclosed in the Schumer box under Regulation Z. The formula:

Finance charge = DPR x ADB x days in cycle

Where:

• DPR (daily periodic rate) = APR divided by 365 (or 360 for some retail cards)
• ADB (average daily balance) = sum of each day’s ending balance, divided by number of days in the cycle
• Days in cycle = typically 28 to 31 days

The output is the dollar amount that posts as Finance Charge on the statement. The CFPB consumer interest explainer walks through the same formula. The Regulation Z legal basis is 12 CFR 1026.7(b), which requires issuers to disclose the periodic rate and the balance computation method on every periodic statement.

How the average daily balance is built

The ADB calculation is mechanical:

1. The issuer records your ending balance for every day in the billing cycle.
2. Each new purchase adds to the daily balance starting on its posting date.
3. Each payment subtracts from the daily balance starting on its posting date.
4. The issuer sums all 28 to 31 daily ending balances.
5. The sum is divided by the number of days in the cycle.

The Federal Reserve Regulation Z Comment 14 describes the accepted balance computation methods. The most common is the average daily balance including new purchases, used by Chase, Citi, Capital One, Bank of America, and Discover. A small number of cards exclude new purchases from ADB (called “average daily balance excluding new purchases”), but this is uncommon post-CARD Act.

Posting date vs transaction date

Interest math runs on posting date, not transaction date. A purchase made on day 10 of a 30 day cycle but posted on day 12 enters ADB on day 12. Most issuers post purchases within 1 to 3 business days of transaction. Payments post within 1 business day if made before the cutoff (typically 5 PM Eastern), 2 business days if made after.

The posting date distinction matters when you push a payment to land before cycle close. A payment made on day 29 but posted on day 31 (after cycle close) affects the NEXT cycle’s ADB, not this one. The OCC’s helpwithmybank.gov page on payment posting confirms the same rule.

Worked example, single rate balance

The pillar APR interest calculator runs the full formula for any APR, balance, and cycle length. A concrete walk-through:

Inputs:

• APR: 22.76 percent (Federal Reserve Q1 2026 average)
• Starting balance: $3,000
• One purchase: $2,000 posted on day 8
• One payment: $500 posted on day 22
• Cycle length: 30 days

Daily balances:

• Days 1 to 7 (7 days): $3,000
• Days 8 to 21 (14 days): $5,000 (after $2,000 purchase)
• Days 22 to 30 (9 days): $4,500 (after $500 payment)

Average daily balance:

• ($3,000 times 7) + ($5,000 times 14) + ($4,500 times 9) = $21,000 + $70,000 + $40,500 = $131,500
• $131,500 divided by 30 = $4,383.33

Finance charge:

• DPR = 0.2276 divided by 365 = 0.0006236
• $4,383.33 times 0.0006236 times 30 = $82.01

The Finance Charge line on the statement reads $82.01 for that cycle.

Two rate calculation, purchases plus cash advance

When a card has different APRs for different balance categories (purchases, cash advances, balance transfers, penalty), the issuer calculates each separately, then sums them on the statement.

Example: $3,500 purchase balance at 22.76 percent purchase APR plus $500 cash advance balance at 28.99 percent cash advance APR, 30 day cycle:

• Purchase finance charge: 0.0006236 times $3,500 times 30 = $65.48
• Cash advance finance charge: 0.0007942 times $500 times 30 = $11.91
• Total finance charge: $77.39

Cash advances generally start accruing immediately with no grace period, per most cardholder agreements. The CFPB cash advance explainer describes the higher APR and immediate accrual.

Three rate calculation: promotional balance transfer

Add a 0 percent intro APR balance transfer:

• $3,500 purchase balance at 22.76 percent
• $500 cash advance balance at 28.99 percent
• $4,000 balance transfer at 0 percent intro APR (12 month promo)

Daily interest calculations:

The 0 percent intro period saves $74.82 per cycle on the $4,000 balance transfer for the duration of the promo. After the intro ends, the standard balance transfer APR (typically 18 to 26 percent) replaces 0 percent. See the 0 APR balance transfer calculator for the full timeline math.

Lower ADB by paying early in the cycle

Every dollar paid down sooner reduces the daily balance for the rest of the cycle. A $500 payment on day 1 lowers ADB by roughly $483 (for a 30 day cycle); the same $500 payment on day 29 lowers ADB by only $17.

Worked savings, $5,000 starting balance at 22.76 percent APR, 30 day cycle, $500 payment timing:

Same payment, $9.04 savings just by timing it to day 1 instead of day 30. The sibling page on mid cycle payments shows the year-long compound effect.

Use the grace period to skip interest entirely

If you pay the full statement balance by the due date, new purchases incur zero finance charge. The grace period typically runs 21 to 25 days from statement close to due date. The grace period applies only to purchases, not cash advances or balance transfers. The CFPB grace period FAQ and the sibling page on grace periods detail the conditions.

Refinance high APR into a lower rate product

At 22.76 percent APR, a $5,000 balance costs roughly $1,277.50 in interest per year under daily compounding. Refinancing into a 12 percent personal loan drops annual interest to roughly $634 per year, savings of $643 per year on the same balance. A 0 percent intro APR balance transfer (typical 3 percent transfer fee, 12 to 21 month promo) trades $150 in transfer fees for one year of zero interest. The debt consolidation calculator compares both paths.

Authoritative sources

• Consumer Financial Protection Bureau, How does my credit card company calculate the amount of interest I have to pay?
• Federal Reserve G.19 Consumer Credit (latest release)
• Regulation Z, 12 CFR 1026.7(b) (Periodic statement disclosures)
• Regulation Z Comment 14 (APR computation)
• Federal Trade Commission, Credit Card Interest
• helpwithmybank.gov, Payment Cutoff Times (OCC)

Sibling questions

• Does credit card interest accrue daily or monthly?
• Does credit card interest compound daily?
• What is the average daily balance method?
• How does daily periodic rate work?

Related tools

• Credit card APR interest calculator for instant finance charge math
• Credit card payoff calculator for full payoff timelines
• Biweekly payment credit card calculator

Frequently asked questions

What is the formula for credit card interest?

Finance charge equals daily periodic rate times average daily balance times days in the billing cycle. The daily periodic rate (DPR) is APR divided by 365. The average daily balance (ADB) is the sum of each day’s ending balance, divided by the number of days in the cycle. For a 22.76 percent APR card with a $4,000 average daily balance over 30 days, the finance charge is 0.0006236 times $4,000 times 30, or $74.82.

What is the average daily balance on a credit card?

Average daily balance (ADB) is the sum of your ending balance for each day in the billing cycle, divided by the number of days in the cycle. If your balance is $3,000 for 15 days then $5,000 for 15 days, your ADB equals ($3,000 times 15 plus $5,000 times 15) divided by 30, which equals $4,000. New purchases that post mid cycle and payments that post mid cycle both affect ADB.

How is the daily periodic rate calculated?

The daily periodic rate (DPR) equals your APR divided by 365 days (some issuers use 360). For the Federal Reserve Q1 2026 average credit card APR of 22.76 percent, the DPR is 0.06236 percent per day. The DPR is multiplied by your average daily balance each day to compute that day’s interest accrual. The DPR appears in your Schumer box under the section on how interest is charged.

Does credit card interest include fees in the calculation?

No. The finance charge calculated from daily periodic rate times average daily balance times days does not include fees. Annual fees, late fees, returned payment fees, and balance transfer fees are added separately to your statement balance, where they then earn interest in subsequent cycles if not paid. Cash advance fees are an exception; cash advances begin accruing interest immediately at a usually higher cash advance APR.

Why is my actual interest charge different from APR times balance?

Because interest accrues daily, not annually, and balances change daily as payments and new charges post. The Schumer box APR is the stated annual rate, but the issuer applies APR divided by 365 to your average daily balance, not to your end-of-month balance. A simple APR times balance shortcut overestimates if your balance grew during the cycle and underestimates if you paid down mid cycle.