How to Calculate Revolving Credit Card Interest

Revolving credit card interest is the cost of borrowing money on a credit card where you can spend and pay back the balance over time. Unlike fixed-term loans, revolving credit allows you to continuously borrow and repay, with interest calculated on the outstanding balance each billing cycle.

What is Revolving Credit Card Interest?

Revolving credit card interest is the daily cost of carrying a balance on your credit card. It's calculated based on your average daily balance and the card's interest rate. Unlike fixed-term loans, revolving credit allows you to spend and repay as needed, with interest accruing on the outstanding amount each billing cycle.

Key Terms

APR (Annual Percentage Rate): The annual cost of borrowing, expressed as a percentage.
Daily Periodic Rate (DPR): The daily interest rate calculated by dividing the APR by 365 or 366.
Average Daily Balance (ADB): The average amount owed during the billing cycle.

Interest Calculation Methods

Most credit cards use the "average daily balance" method, where interest is calculated on the average balance each day of the billing cycle. Some cards may use the "previous balance" method, where interest is calculated on the balance at the start of the cycle.

How to Calculate Revolving Interest

Calculating revolving interest involves several steps to determine the total interest charged over a billing cycle. Here's the step-by-step process:

Step 1: Determine the Daily Periodic Rate

First, convert the APR to a daily rate by dividing by 365 or 366 (accounting for leap years).

Daily Periodic Rate Formula

DPR = APR / 365

Step 2: Calculate the Average Daily Balance

Sum the daily balances for the billing cycle and divide by the number of days in the cycle.

Average Daily Balance Formula

ADB = (Sum of daily balances) / Number of days in billing cycle

Step 3: Compute the Daily Interest Charge

Multiply the average daily balance by the daily periodic rate.

Daily Interest Charge Formula

Daily Interest = ADB × DPR

Step 4: Calculate the Total Interest for the Billing Cycle

Multiply the daily interest charge by the number of days in the billing cycle.

Total Interest Formula

Total Interest = Daily Interest × Number of days in billing cycle

Step 5: Add the Interest to Your Previous Balance

The total interest is added to your previous balance to determine the new balance due.

Example Calculation

Let's walk through an example to see how revolving interest is calculated.

Example Scenario

Credit card APR: 18% (0.18)
Billing cycle: 30 days
Daily balances:
- Day 1: $1,000
- Day 2: $1,200
- Day 3: $1,500
- ... (assuming a consistent pattern)
- Day 30: $3,000

Step-by-Step Calculation

Calculate the daily periodic rate:
DPR = 0.18 / 365 ≈ 0.000493 (0.0493%)
Calculate the average daily balance:
ADB = ($1,000 + $1,200 + $1,500 + ... + $3,000) / 30 ≈ $2,000
Calculate the daily interest charge:
Daily Interest = $2,000 × 0.000493 ≈ $0.986
Calculate the total interest for the billing cycle:
Total Interest = $0.986 × 30 ≈ $29.58

Result

For this example, the total interest charged would be approximately $29.58 over the 30-day billing cycle.

Interest vs. Balance

Understanding the relationship between interest and balance is crucial for managing your credit card debt effectively.

Key Relationships

Higher balances generate more interest: The more you owe, the more interest you'll accrue.
Longer payment periods increase interest: Carrying a balance for more days in the billing cycle will result in higher interest charges.
Interest compounds over time: If you don't pay off your balance in full each month, the interest will accumulate and increase your debt.

Comparison Table

Balance	APR (18%)	Interest (30 days)
$1,000	18%	$17.58
$2,000	18%	$35.16
$3,000	18%	$52.74

This table shows how interest grows with larger balances at the same APR. It's clear that reducing your balance can significantly lower your interest charges.

FAQ

How is revolving interest different from fixed-term interest?

Revolving interest is calculated on your average daily balance and can change each billing cycle, while fixed-term interest is calculated on a set principal amount with a fixed repayment schedule.

Can I avoid revolving interest?

Yes, by paying your balance in full each month before the statement date, you can avoid interest charges. Many credit cards offer interest-free periods if you pay on time.

How does the grace period affect revolving interest?

The grace period is the time between when you receive your statement and when interest starts accruing. If you pay your balance in full during this period, you won't be charged interest.

What happens if I miss a payment?

Missing a payment can result in late fees, higher interest rates, and potential damage to your credit score. It's important to make payments on time to avoid these consequences.