{
  "id": "daily-interest",
  "version": "c86743a80616",
  "status": "published",
  "name": "Daily Interest Calculator",
  "question": "How much daily interest will I get?",
  "summary": "Computes the interest a balance earns or owes each day (annual rate ÷ 365, 360 or 366) and the total over a number of days, as simple interest or compounded daily, with the APY.",
  "category": "finance",
  "subcategory": "investing",
  "url": "https://www.acalculator.org/finance/daily-interest-calculator",
  "markdown": "https://www.acalculator.org/finance/daily-interest-calculator.md",
  "kind": "function",
  "method": "Daily rate = annual rate ÷ days in a year. Simple: interest = balance × annual rate × days ÷ days in a year. Daily compounding: interest = balance × ((1 + annual rate ÷ days in a year)^days − 1). APY = 100 × ((1 + interest ÷ balance)^(365 ÷ days) − 1).",
  "assumptions": [
    "The balance does not change during the days, apart from interest added daily when compounding.",
    "The rate is read to 6 decimal places of a percent; each money amount is worked out exactly, and its shown cents are the exact value rounded half up.",
    "No fees, deposits, withdrawals or payments."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "p": {
        "title": "Balance",
        "description": "The amount the interest is worked out on: a savings balance or a loan balance.",
        "type": "number",
        "x-unit": "USD",
        "minimum": 0.01,
        "maximum": 1000000000000
      },
      "r": {
        "title": "Annual interest rate",
        "description": "The yearly interest rate, before dividing by the days in a year.",
        "type": "number",
        "x-unit": "percent",
        "minimum": 0,
        "maximum": 100
      },
      "days": {
        "title": "Number of days",
        "description": "How many days the balance earns or owes interest.",
        "type": "integer",
        "minimum": 1,
        "maximum": 3660
      },
      "m": {
        "title": "Interest",
        "description": "Simple interest on the balance only, or interest added to the balance every day (compounded daily).",
        "type": "string",
        "enum": [
          "simple",
          "daily"
        ]
      },
      "basis": {
        "title": "Days in a year",
        "description": "The days the annual rate is divided by: 365 for most savings accounts, 360 for many loans.",
        "type": "string",
        "enum": [
          "365",
          "360",
          "366"
        ]
      }
    }
  },
  "outputs": {
    "interest": {
      "label": "Total interest",
      "description": "The interest over all the days.",
      "format": "money"
    },
    "daily": {
      "label": "Interest for one day",
      "description": "The first day’s interest: balance × annual rate ÷ days in a year.",
      "format": "money"
    },
    "balance": {
      "label": "Balance after the days",
      "description": "The starting balance plus the total interest.",
      "format": "money"
    },
    "dailyRate": {
      "label": "Daily rate",
      "description": "The annual rate ÷ the days in a year.",
      "format": "percent"
    },
    "apy": {
      "label": "Annual percentage yield",
      "description": "The yearly yield this interest gives, by the Regulation DD formula: 100 × ((1 + interest ÷ balance)^(365 ÷ days) − 1).",
      "format": "percent"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "p": 10000,
      "r": 5,
      "days": 30,
      "m": "simple",
      "basis": "365"
    },
    "outputs": {
      "interest": 41.0958904109589,
      "daily": 1.36986301369863,
      "balance": 10041.09589041096,
      "dailyRate": 0.0136986301369863,
      "apy": 5.116338959082456
    },
    "text": "$10,000.00 at 5% for 30 days earns $41.10 of interest, $1.37 a day."
  },
  "examples": [
    {
      "given": {
        "p": 10000,
        "r": 5,
        "days": 30,
        "m": "simple",
        "basis": "365"
      },
      "expect": {
        "daily": 1.36986301369863,
        "interest": 41.0958904109589,
        "balance": 10041.09589041096,
        "apy": 5.116338959082456
      },
      "source": "CFPB Regulation DD, 12 CFR 1030.7: interest by a daily rate of at least 1/365 of the interest rate (https://www.consumerfinance.gov/rules-policy/regulations/1030/7/, retrieved 2026-10-01); APY formula from 12 CFR 1030 Appendix A (https://www.consumerfinance.gov/rules-policy/regulations/1030/a/); hand calculation in content.mdx",
      "tolerance": 1e-11
    },
    {
      "given": {
        "p": 1000,
        "r": 6,
        "days": 365,
        "m": "daily",
        "basis": "365"
      },
      "expect": {
        "interest": 61.831310677853686,
        "apy": 6.1831310677853635
      },
      "source": "CFPB Regulation DD, 12 CFR 1030 Appendix A: APY = 100 [(1 + Interest/Principal)^(365/Days in term) − 1], and for a 365-day term APY = 100 (Interest/Principal) (https://www.consumerfinance.gov/rules-policy/regulations/1030/a/, retrieved 2026-10-01); Python 3 fractions cross-check",
      "tolerance": 1e-11
    },
    {
      "given": {
        "p": 50000,
        "r": 7.25,
        "days": 90,
        "m": "simple",
        "basis": "360"
      },
      "expect": {
        "interest": 906.25,
        "daily": 10.069444444444445,
        "dailyRate": 0.02013888888888889
      },
      "source": "CFPB Regulation DD, 12 CFR 1030.7 (daily rate); hand calculation in content.mdx: 50,000 × 0.0725 × 90 ÷ 360 = 906.25",
      "tolerance": 1e-11
    },
    {
      "given": {
        "p": 2500,
        "r": 18,
        "days": 31,
        "m": "daily",
        "basis": "365"
      },
      "expect": {
        "interest": 38.503247702623256
      },
      "source": "CFPB Regulation DD, 12 CFR 1030.7 (daily rate of 1/365 of the rate); hand calculation in content.mdx: 2,500 × ((1 + 0.18 ÷ 365)^31 − 1)",
      "tolerance": 1e-11
    }
  ],
  "sources": [
    "Consumer Financial Protection Bureau, Regulation DD (Truth in Savings), 12 CFR 1030.7, Payment of interest: interest by a daily rate of at least 1/365 of the interest rate, or 1/366 in a leap year, retrieved 2026-10-01. https://www.consumerfinance.gov/rules-policy/regulations/1030/7/",
    "Consumer Financial Protection Bureau, Regulation DD, 12 CFR 1030 Appendix A, Annual Percentage Yield Calculation: APY = 100 [(1 + Interest/Principal)^(365/Days in term) − 1], retrieved 2026-10-01. https://www.consumerfinance.gov/rules-policy/regulations/1030/a/"
  ],
  "related": [
    "simple-interest",
    "compound-interest",
    "interest"
  ],
  "changelog": []
}