Credit Card Interest Calculator
On a 30-day cycle at 24% APR, a $1,000 start balance and our default changes give a $1,066.67 average daily balance. That costs $21.04 in interest.
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Your cycle interest and average daily balance
Daily Periodic Rate
0.06575%
Average Daily Balance
$1,066.67
Interest Charged
$21.04
On a $1,066.67 average daily balance at 24% APR, your 30-day cycle costs $21.04 in interest.
Your 365-day daily rate is 0.06575%, and the new balance with interest is $721.04.
Daily compounding at the same rate costs $21.26 ($0.21 more). A 360-day year costs $21.33 ($0.29 more).
Your card terms and cycle activity
- daily periodic rate = 24% ÷ 365 ≈ 0.06575%
- balance-days = $1,000.00 × 10 + $1,500.00 × 10 + $700.00 × 10 = $32,000.00
- average daily balance = $32,000.00 ÷ 30 ≈ $1,066.67
- interest = $1,066.67 × 0.06575% × 30 ≈ $21.04
Balance on each stretch of the billing cycle
Interest across Regulation Z balance methods
Interest for the cycle at each APR
Across APRs from 10% to 29.99% on your cycle balances, interest rises from $8.77 to $26.29.
| APR | Daily Periodic Rate | Interest Charged |
|---|---|---|
| 10% | 0.02740% | $8.77 |
| 12% | 0.03288% | $10.52 |
| 15% | 0.04110% | $13.15 |
| 18% | 0.04932% | $15.78 |
| 20% | 0.05479% | $17.53 |
| 22% | 0.06027% | $19.29 |
| 24% (closest to your input) | 0.06575% | $21.04 |
| 26% | 0.07123% | $22.79 |
| 28% | 0.07671% | $24.55 |
| 29.99% | 0.08216% | $26.29 |
Interest charged, by APR (down) and balance on day 1 (across), with every other input as entered above.
| APR by balance on day 1 | $500 | $1,000 | $1,500 | $2,500 | $5,000 |
|---|---|---|---|---|---|
| 10% | $4.66 | $8.77 | $12.88 | $21.10 | $41.64 |
| 12% | $5.59 | $10.52 | $15.45 | $25.32 | $49.97 |
| 15% | $6.99 | $13.15 | $19.32 | $31.64 | $62.47 |
| 18% | $8.38 | $15.78 | $23.18 | $37.97 | $74.96 |
| 20% | $9.32 | $17.53 | $25.75 | $42.19 | $83.29 |
| 22% | $10.25 | $19.29 | $28.33 | $46.41 | $91.62 |
| 24% (closest to your input) | $11.18 | $21.04 | $30.90 | $50.63 | $99.95 |
| 26% | $12.11 | $22.79 | $33.48 | $54.85 | $108.27 |
| 28% | $13.04 | $24.55 | $36.05 | $59.07 | $116.60 |
| 29.99% | $13.97 | $26.29 | $38.62 | $63.27 | $124.89 |
Interest across 28 to 32-day billing cycles
Moving from a 28-day February cycle to a 32-day cycle changes your finance charge from $20.12 to $21.96.
| Cycle days | Average Daily Balance | Interest Charged |
|---|---|---|
| 28 days | $1,092.86 | $20.12 |
| 29 days | $1,079.31 | $20.58 |
| 30 days (closest to your input) | $1,066.67 | $21.04 |
| 31 days | $1,054.84 | $21.50 |
| 32 days | $1,043.75 | $21.96 |
Daily Balances
| From day | To day | Days | Balance | Balance × days |
|---|---|---|---|---|
| 1 | 10 | 10 | $1,000.00 | $10,000.00 |
| 11 | 20 | 10 | $1,500.00 | $15,000.00 |
| 21 | 30 | 10 | $700.00 | $7,000.00 |
Your cycle splits into 3 stretches totaling $32,000.00 of balance-days, or $1,066.67 per day over 30 days.
Balance Methods Compared
| Computation method | Balance subject to rate | Daily rate (%) | Interest charged | Vs. your method |
|---|---|---|---|---|
| Average daily balance (365-day year, simple) | $1,066.67 | 0.06575 | $21.04 | $0.00 |
| Average daily balance (360-day year, simple) | $1,066.67 | 0.06667 | $21.33 | $0.29 |
| Daily balance with daily compounding (365-day year) | $1,066.67 | 0.06575 | $21.26 | $0.21 |
| Daily balance with daily compounding (360-day year) | $1,066.67 | 0.06667 | $21.55 | $0.51 |
| Adjusted balance (Appendix G-1(A)(a)) | $200.00 | 0.06575 | $3.95 | -$17.10 |
| Previous balance (Appendix G-1(A)(b)) | $1,000.00 | 0.06575 | $19.73 | -$1.32 |
Across Regulation Z balance methods on these figures, cycle interest ranges from $3.95 to $21.55.
How credit card interest works
As CFPB answer #51 notes, “Many issuers calculate the interest you owe daily, based on the average daily balance.” To get a daily rate, the card divides your APR by 360 or 365, depending on the issuer, as CFPB answer #46 explains. At 24% APR on a 365-day year, the daily rate is 24% ÷ 365 = 0.06575%.
Each day of the billing cycle, the card records your end-of-day balance. It starts with day 1, adds new purchases, and subtracts payments posted on or before that day. It then adds all daily balances and divides by the days in the cycle to get the average daily balance under 12 CFR 1026.7(b)(5).
Every day has the same weight in that sum, so timing matters. A purchase posted on day 11 sits on the card for 20 of the 30 days. A payment posted on day 21 trims only the last 10 days. Multiply the average daily balance by the daily rate and the cycle days to find the charge.
Regulation Z balance methods
Appendix G to 12 CFR part 1026 (Model Clauses G-1 and G-1(A)) sets out four main balance methods for card plans. Average daily balance (including current transactions) adds new purchases on the day they post and subtracts payments as they arrive. Under Appendix G-1(A)(d), the card divides the sum of those daily balances by the number of days in the billing cycle.
The other three Appendix G methods give different results on the default 30-day cycle. Average daily balance (excluding current transactions) leaves out new purchases under Appendix G-1(A)(c). That gives a $733.33 average daily balance and $14.47 of interest. Under the adjusted balance method in Appendix G-1(A)(a), the $800 payment comes off the $1,000 start balance first, leaving $200.00 and $3.95 of interest. Under the previous balance method in Appendix G-1(A)(b), the rate applies to the full $1,000 day-1 balance ($19.73).
Appendix F to 12 CFR part 1026 gives a test case in Example 2. A 30-day cycle starts at $100, adds a $100 purchase on day 10 for 20 days, and takes a $75 payment on day 20 for 10 days. The 30 daily balances add up to $4,250 ($1,000 + $2,000 + $1,250). Divided by 30 days, the average daily balance is $141.67 ($141.6667 unrounded). You can check interest on a fixed loan balance between two dates in the daily interest calculator.
Daily compounding and 365 vs. 360-day years
Under Regulation Z comment 7(b)(5)-4 and Appendix G-1(A)(f), a card may use the daily balance method with daily compounding. Instead of multiplying once at the end of the month, the card figures interest each night and adds it to the next day's balance. On the default 30-day cycle at 24% APR, daily compounding raises the charge from $21.04 to $21.26. That is an extra $0.22.
On a flat $1,000 held for 30 days at 24% APR, simple average daily balance costs $19.73. Daily compounding costs $19.92 (19 cents more). Over a full year with no payments, daily compounding turns a 24% APR into a 27.11% yearly yield. Even when a card compounds daily, Regulation Z comment 7(b)(5)-4 lets the bill print the simple average daily balance when the dollar charge is exact.
As CFPB answer #46 states, the daily rate can be found “by dividing the annual percentage rate, or APR, by either 360 or 365, depending on the card issuer.” On the default cycle, a 360-day year raises the charge to $21.33 ($0.29 above the 365-day figure). In the Federal Reserve's G.19 report for August 2026 (released October 7, 2026), bank card plans averaged 22.36% APR on accounts charged interest (22.32% in 2025). Across all card accounts, the average rate was 21.19% (21.22% in 2025).
Video walkthrough
A 2½-minute walkthrough of how a card works out a cycle's interest, and what the day you pay changes.
Read the transcript
How credit card interest adds up
0:00 Carry $1,000 at 24% for a 30-day cycle, and the interest builds up day after day.
0:07 In this example the charge comes to about $21.
0:11 Pay earlier in that cycle, and the charge is halved.
0:14 That charge is not one monthly fee.
0:17 As the CFPB's answer says, many issuers calculate the interest you owe daily, based on the average daily balance.
0:24 The charge is worked out in steps: the APR, your card's yearly rate, becomes a daily rate.
0:31 Then each day's balance joins the running total.
0:34 Those daily balances add up over the whole cycle.
0:37 Divide the total by the cycle's days, and that is the average daily balance.
0:42 Multiply that average by the daily rate and the days.
0:45 That gives the cycle's interest.
Why the day you pay matters
0:48 Picture the cycle day by day: the purchase posts on day 11.
0:52 The balance steps up.
0:53 The payment lands on day 21.
0:56 The balance steps down.
0:57 The purchase remains 20 of the 30 days: the payment trims only the last 10 days.
1:03 Move that payment to the cycle's first day and press Calculate.
1:07 The balance-days halve to $16,000, the average balance drops to about $530, and the charge you owe then falls to about $11.
Why the bill can run a little high
1:18 The statement can run slightly above the simple charge, and this is why.
1:22 Some cards add each day's interest to the balance so the interest compounds daily.
1:27 Some issuers divide the year into 360 days instead of the calendar year.
1:33 Your statement's interest box names the balance the card applied the rate to: the Balance Subject to Interest Rate.
1:40 Compare that figure with the average daily balance from those steps.
Try your own numbers
1:44 To check your own bill, switch the balance entry to your statement's average.
1:49 Type in the average your statement prints, about $1,100 here, and the simple interest charge matches the day-by-day run.
1:57 One table lists the balance for each stretch of the cycle, up to $1,500.
2:02 Copy the link and revisit these numbers later.
Before you carry a balance
2:06 This example carries a balance through the cycle, so interest runs every day.
2:11 A grace period, the window after your own cycle's end, runs until your payment's due date.
2:16 With a grace period, paying the entire balance by each month's due date means new purchases add no interest.
2:23 So: each day's balance counts, pay earlier in the cycle, and check the charge on your bill.
2:29 Try your own cycle at fastcalc.us.
Average daily balance and periodic rate formulas
daily periodic rate = APR ÷ 100 ÷ days in year (365 or 360) balance_d = max(0, day-1 balance + Σ changes posted on or before day d) average daily balance = (Σ balance_d for d = 1..N) ÷ N simple cycle interest = average daily balance × daily periodic rate × N daily compounded interest = Σ (accrued_balance_d × daily periodic rate) for d = 1..N
Worked billing cycle examples
A 30-day cycle starts at $1,000. A $500 purchase posts on day 11 and an $800 payment on day 21. The balance is $1,000 for 10 days ($10,000), $1,500 for 10 days ($15,000), and $700 for 10 days ($7,000): $32,000 of balance-days, or an average daily balance of $1,066.67.
At 24% APR, multiplying the $1,066.67 average daily balance by 0.0657534% per day over 30 days gives $21.04 of simple interest. The daily compounding section above shows the $21.26 compounded charge. Paying on day 1 instead of day 21 lowers the charge to $10.52.
Month length changes the charge even when your balance stays flat. Holding $1,000 for a 31-day month at 24% APR costs $20.38, while a 28-day February cycle costs $18.41 ($1.97 less).
Grace periods, trailing interest, and the two-cycle ban
As CFPB answer #47 explains, “A grace period is the period between the end of a billing cycle and the date your payment is due.” Under 12 CFR 1026.5(b)(2)(ii), a card with a grace period must send the bill at least 21 days before the due date. You can check those dates in the credit card due date rule calculator. If you pay the prior bill in full on time, new purchases cost $0.00 in interest. Carry even $1.00 past the due date, and you lose the grace period for that month and the next.
Losing your grace period also brings trailing (or residual) interest. Interest builds up each day between the statement closing date and the day your payment posts. If you pay a carried $1,000 bill in full 15 days after the statement closes, those 14 days at 24% APR still leave $9.21 of interest for the next bill. Cash advances have no grace period. They build interest from day 1, often at 26% to 29.99% APR plus a 3% to 5% fee.
Regulation Z (12 CFR 1026.54(a)(1)) bans two-cycle (double-cycle) billing. A card cannot reach back into the prior billing cycle to charge interest on days before the current cycle. Also, under Regulation Z comment 54(a)(1)-5, suppose you start with a grace period and pay $400 of a $1,000 bill by the due date. The card cannot charge trailing interest on the $400 paid on time; only the unpaid $600 carries into the new cycle's balance.
Payment timing, statement checks, and payoff tools
Because the average daily balance weights each dollar by the days it stays on the card, paying early saves money. In the default 30-day cycle at 24% APR, moving the $800 payment from day 21 to day 1 drops the average daily balance to $533.33. That cuts the interest in half to $10.52. Splitting the payment into two $400 payments on days 15 and 29 gives a $1,093.33 average daily balance and $21.57 of interest.
To check your own bill, find the interest charge table required by 12 CFR 1026.7(b)(4). Switch Balance Entry to Average daily balance from my statement and enter the “Balance Subject to Interest Rate” for purchases. If your bill has separate lines for Purchases, Cash Advances, and Balance Transfers, run each line at its own APR and add the charges.
Once you know your monthly interest, compare ways to clear the debt. Use the credit card minimum payment calculator for the 36-month payoff box, or the credit card payoff calculator for a fixed payment. Try the balance transfer calculator to weigh a fee against a promo rate. You can also use the debt payoff calculator or the personal loan calculator to compare payoff plans.
Assumptions and regulatory boundaries
- The main card shows simple average daily balance interest under 12 CFR part 1026 Appendix G-1(A)(d). The comparison table adds daily compounding under Appendix G-1(A)(f), 360-day year interest, adjusted balance, and previous balance.
- No grace period is applied here. Under 12 CFR 1026.54, paying your prior bill in full by the due date avoids purchase interest. This tool models a balance that is being charged interest.
- One APR is applied to the balance. If your statement lists separate purchase, cash-advance, and transfer balances under 12 CFR 1026.7(b)(5), run each line at its own APR.
- Credit balances below $0.00 count as $0.00 for that day, since cards do not pay interest on a credit balance.
- The default 24% APR is an example rate. In the August 2026 Federal Reserve G.19 release, bank cards charged interest averaged 22.36% APR.
These figures are estimates for learning and planning, not financial, tax, legal or investment advice. Terms of use.
What to do with your statement numbers
Check your bill's “Balance Subject to Interest Rate” box. If your statement charge is $0.15 to $0.35 higher than our simple result, check the method table above for daily compounding or a 360-day year.
Pay early in the cycle when you carry a balance. Making your payment on day 1 instead of day 21 cuts the default 30-day interest charge by 50% (saving $10.52 at 24% APR).
Look out for trailing interest after you pay off a carried balance. Paying a $1,000 bill in full on day 15 still leaves 14 days of interest ($9.21 at 24% APR) on the next statement.
Lower your rate and your credit limit ratio together. Keeping utilization below 30% in the credit utilization calculator helps you qualify for a 0% offer in the balance transfer calculator.
Frequently asked questions
How do I calculate credit card interest per month?
Divide your APR by 365 to get the daily rate, then multiply by your average daily balance and by the days in the cycle. On a $1,000 flat balance over 30 days at 24% APR, the charge is $19.73.
How much interest will I pay on a $5,000 credit card balance?
At the August 2026 Federal Reserve G.19 rate of 22.36% APR, $5,000 held for 30 days costs $91.89 ($92.73 with daily compounding). At 22% APR over 30 days, the charge is $90.41.
What is the daily periodic rate on a 24% APR?
Dividing 24% APR by a 365-day year gives 0.06575% a day, while a 360-day year gives 0.06667% a day. Over 30 days on a $1,000 balance, that 360-day rate costs $20.00 instead of $19.73 ($0.27 more).
Why is my statement's interest charge slightly higher than simple ADB?
Under Regulation Z Appendix G-1(A)(f), an issuer may compound interest each day or divide by a 360-day year. On the default 30-day cycle at 24% APR, daily compounding adds $0.22 (reaching $21.26), and a 360-day year brings the simple charge to $21.33.
Does paying earlier in the billing cycle reduce credit card interest?
Yes. Each day a payment posts earlier takes that amount off every remaining day of the cycle. In the 30-day default case at 24% APR, paying on day 1 instead of day 21 drops the average daily balance in half to $533.33 and lowers interest to $10.52.
Do I pay interest if I pay my statement balance in full each month?
Not on purchases when your card has a grace period and you paid the prior bill in full on time. New purchases then cost $0.00. If you pay even $1.00 short, you lose the grace period for that cycle and the next cycle.
What is double-cycle billing and is it legal?
Double-cycle (two-cycle) billing reached back into the prior billing cycle to charge interest when you lost a grace period. Regulation Z (12 CFR 1026.54) banned two-cycle billing on consumer cards, saving $19.73 of prior-cycle interest per $1,000 at 24% APR.
Sources
- Regulation Z, 12 CFR 1026.7(b)(5), balance on which interest is computed (CFPB text) (current version)
- Regulation Z, 12 CFR 1026.54, limitations on the imposition of finance charges (CFPB text) (current version)
- Regulation Z, Appendix F to Part 1026, optional annual percentage rate computations (CFPB text) (current version)
- Regulation Z, Appendix G to Part 1026, open-end model forms and clauses (CFPB text) (current version)
- CFPB, How does my credit card company calculate the amount of interest I owe? (page reviewed Jan 22, 2024)
- CFPB, What is a daily periodic rate on a credit card? (page reviewed Sep 23, 2024)
- CFPB, What is a grace period for a credit card? (page reviewed Sep 23, 2024)
- Federal Reserve, G.19 Consumer Credit, August 2026 (page modified Oct 7, 2026)
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