{
  "id": "average-daily-balance",
  "version": "2782e5e8b0d2",
  "status": "published",
  "name": "Average Daily Balance Calculator",
  "question": "What is my average daily balance?",
  "summary": "Works out a credit card’s average daily balance for a billing cycle (the sum of the daily balances ÷ the days) and the interest at a daily periodic rate of APR ÷ 365.",
  "category": "finance",
  "subcategory": "loans",
  "url": "https://www.acalculator.org/finance/average-daily-balance-calculator",
  "markdown": "https://www.acalculator.org/finance/average-daily-balance-calculator.md",
  "kind": "function",
  "method": "Average daily balance = Σ (balance × days) ÷ Σ days. Daily periodic rate = APR ÷ 365 (or ÷ 360). Interest for the cycle = average daily balance × days in the cycle × daily periodic rate ÷ 100.",
  "assumptions": [
    "Each balance is the end-of-day balance after that day’s purchases, fees, payments and credits (the method that includes current transactions).",
    "No compounding within the cycle: the interest is not added to the daily balances.",
    "Arithmetic is exact on the typed decimals; money shows to the cent, halves rounded up."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "periods": {
        "title": "Balances in the billing cycle",
        "description": "Each balance the account had during the cycle, after that day’s purchases, payments and credits, and for how many days.",
        "type": "array",
        "items": {
          "type": "object",
          "properties": {
            "b": {
              "title": "Balance",
              "description": "The end-of-day balance for these days.",
              "type": "number",
              "x-unit": "USD",
              "minimum": 0,
              "maximum": 1000000000
            },
            "d": {
              "title": "Days",
              "description": "How many days of the cycle the balance stayed at this amount.",
              "type": "integer",
              "minimum": 1,
              "maximum": 366
            }
          }
        }
      },
      "apr": {
        "title": "APR",
        "description": "The card’s annual percentage rate, for the interest. Optional.",
        "type": "number",
        "x-unit": "percent",
        "minimum": 0,
        "maximum": 100
      },
      "basis": {
        "title": "Days in the year",
        "description": "The daily periodic rate is APR ÷ 365, or APR ÷ 360 for card issuers that use 360 days.",
        "type": "string",
        "enum": [
          "365",
          "360"
        ]
      }
    }
  },
  "outputs": {
    "average": {
      "label": "Average daily balance",
      "description": "The sum of the daily balances ÷ the days in the cycle.",
      "format": "money"
    },
    "days": {
      "label": "Days in the billing cycle",
      "description": "The days of all the rows added up.",
      "format": "integer"
    },
    "sum": {
      "label": "Sum of the daily balances",
      "description": "Each balance × its days, added up.",
      "format": "money"
    },
    "dailyRate": {
      "label": "Daily periodic rate",
      "description": "APR ÷ 365 (or ÷ 360). Shown when an APR is typed.",
      "format": "percent"
    },
    "interest": {
      "label": "Interest for the cycle",
      "description": "Average daily balance × days × daily periodic rate ÷ 100. Shown when an APR is typed.",
      "format": "money"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "periods": [
        {
          "balance": "1000",
          "days": 10
        },
        {
          "balance": "1500",
          "days": 15
        },
        {
          "balance": "700",
          "days": 5
        }
      ],
      "apr": 24,
      "basis": "365"
    },
    "outputs": {
      "average": 1200,
      "days": 30,
      "sum": 36000,
      "dailyRate": 0.06575342465753424,
      "interest": 23.671232876712327
    },
    "text": "Over 30 days the average daily balance is $1,200.00."
  },
  "examples": [
    {
      "given": {
        "periods": [
          {
            "balance": "1000",
            "days": 10
          },
          {
            "balance": "1500",
            "days": 15
          },
          {
            "balance": "700",
            "days": 5
          }
        ],
        "apr": 24,
        "basis": "365"
      },
      "expect": {
        "average": 1200,
        "days": 30,
        "sum": 36000,
        "dailyRate": 0.06575342465753424,
        "interest": 23.671232876712327
      },
      "source": "CFPB, Regulation Z (12 CFR part 1026), Appendix G-1(A), clause (d), Average Daily Balance Method (Including Current Transactions), https://www.consumerfinance.gov/rules-policy/regulations/1026/g/; CFPB, Regulation Z, comment 7(b)(5)-4.i.D (average daily balance × days in the cycle × periodic rate), https://www.consumerfinance.gov/rules-policy/regulations/1026/interp-7/; hand calculation in content.mdx; Python 3 check in docs/progress/WP-137/xcheck.py: 36,000 ÷ 30 = 1,200; 1,200 × 30 × 24% ÷ 365 = 23.67"
    },
    {
      "given": {
        "periods": [
          {
            "balance": "500",
            "days": 31
          }
        ],
        "apr": 18,
        "basis": "365"
      },
      "expect": {
        "average": 500,
        "days": 31,
        "interest": 7.6438356164383565
      },
      "source": "CFPB, Regulation Z (12 CFR part 1026), Appendix G-1(A), clause (d), Average Daily Balance Method (Including Current Transactions), https://www.consumerfinance.gov/rules-policy/regulations/1026/g/; CFPB, Regulation Z, comment 7(b)(5)-4.i.D (average daily balance × days in the cycle × periodic rate), https://www.consumerfinance.gov/rules-policy/regulations/1026/interp-7/; hand calculation in content.mdx; Python 3 check in docs/progress/WP-137/xcheck.py: a balance that never changes is its own average; 500 × 31 × 18% ÷ 365 = 7.64"
    },
    {
      "given": {
        "periods": [
          {
            "balance": "0",
            "days": 12
          },
          {
            "balance": "2500.5",
            "days": 18
          }
        ],
        "basis": "365"
      },
      "expect": {
        "average": 1500.3,
        "days": 30,
        "sum": 45009
      },
      "source": "CFPB, Regulation Z (12 CFR part 1026), Appendix G-1(A), clause (d), Average Daily Balance Method (Including Current Transactions), https://www.consumerfinance.gov/rules-policy/regulations/1026/g/; hand calculation in content.mdx; Python 3 check in docs/progress/WP-137/xcheck.py: (0 × 12 + 2,500.50 × 18) ÷ 30 = 1,500.30"
    },
    {
      "given": {
        "periods": [
          {
            "balance": "1000",
            "days": 10
          },
          {
            "balance": "1500",
            "days": 15
          },
          {
            "balance": "700",
            "days": 5
          }
        ],
        "apr": 24,
        "basis": "360"
      },
      "expect": {
        "average": 1200,
        "dailyRate": 0.06666666666666667,
        "interest": 24
      },
      "source": "CFPB, Regulation Z, comment 7(b)(5)-4.i.D (average daily balance × days in the cycle × periodic rate), https://www.consumerfinance.gov/rules-policy/regulations/1026/interp-7/; hand calculation in content.mdx; Python 3 check in docs/progress/WP-137/xcheck.py: 1,200 × 30 × 24% ÷ 360 = 24"
    }
  ],
  "sources": [
    "Consumer Financial Protection Bureau, Regulation Z (12 CFR part 1026), Appendix G-1(A), clause (d), Average Daily Balance Method (Including Current Transactions): each day’s balance adds new purchases and subtracts payments and credits; the daily balances are added and divided by the number of days in the billing cycle, and the periodic rate is applied to that average. https://www.consumerfinance.gov/rules-policy/regulations/1026/g/ (retrieved 2026-10-19)",
    "Consumer Financial Protection Bureau, Regulation Z, official interpretation of § 1026.7, comment 7(b)(5)-4.i.D: the average daily balance multiplied by the number of days in the billing cycle and the periodic rate gives the interest. https://www.consumerfinance.gov/rules-policy/regulations/1026/interp-7/ (retrieved 2026-10-19)",
    "Consumer Financial Protection Bureau, Credit card contract definitions: the daily periodic rate is the APR divided by 365. https://www.consumerfinance.gov/data-research/credit-card-data/know-you-owe-credit-cards/credit-card-contract-definitions/ (retrieved 2026-10-19)",
    "Consumer Financial Protection Bureau, Ask CFPB, What is a “daily periodic rate” on a credit card?: the APR divided by 360 or 365, depending on the card issuer. https://www.consumerfinance.gov/ask-cfpb/what-is-a-daily-periodic-rate-on-a-credit-card-en-46/ (retrieved 2026-10-19)",
    "Consumer Financial Protection Bureau, Ask CFPB, How does my credit card company calculate the amount of interest I owe?: many issuers charge interest daily on the average daily balance; paying earlier lowers it; a grace period usually covers new purchases when the full balance is paid by the due date. https://www.consumerfinance.gov/ask-cfpb/how-does-my-credit-card-company-calculate-the-amount-of-interest-i-owe-en-51/ (retrieved 2026-10-19)"
  ],
  "related": [
    "credit-card-interest",
    "credit-card-payoff",
    "minimum-payment"
  ],
  "changelog": []
}