{
  "id": "inflation",
  "version": "deab82c119b1",
  "status": "published",
  "name": "Inflation Calculator",
  "question": "What is a dollar worth after inflation?",
  "summary": "Converts dollars from one month to another since 1913 with the US CPI-U (BLS), with the total and yearly inflation.",
  "category": "finance",
  "subcategory": "investing",
  "url": "https://www.acalculator.org/finance/inflation-calculator",
  "markdown": "https://www.acalculator.org/finance/inflation-calculator.md",
  "kind": "function",
  "method": "Value = amount × end CPI ÷ start CPI; yearly rate = (CPI ratio)^(12 ÷ months) − 1.",
  "assumptions": [
    "CPI-U, all items, US city average, not seasonally adjusted (BLS series CUUR0000SA0).",
    "Each date stands for its month; the day is ignored.",
    "October 2025 has no CPI (BLS did not collect it)."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "amount": {
        "title": "Amount",
        "description": "The dollar amount in the start month.",
        "type": "number",
        "x-unit": "USD",
        "minimum": 0,
        "maximum": 1000000000000
      },
      "from": {
        "title": "In (start month)",
        "description": "Any day of the month, from January 1913.",
        "type": "string",
        "format": "date"
      },
      "to": {
        "title": "Is worth in (end month)",
        "description": "Any day of the month, up to August 2026.",
        "type": "string",
        "format": "date"
      }
    }
  },
  "outputs": {
    "value": {
      "label": "Worth in the end month",
      "description": "Amount × end CPI ÷ start CPI.",
      "format": "money"
    },
    "inflation": {
      "label": "Total inflation",
      "description": "The price change between the months.",
      "format": "percent"
    },
    "yearlyRate": {
      "label": "Average inflation a year",
      "description": "The yearly rate that compounds to the total.",
      "format": "percent"
    },
    "startCpi": {
      "label": "CPI in the start month",
      "description": "CPI-U, 1982-84 = 100.",
      "format": "number"
    },
    "endCpi": {
      "label": "CPI in the end month",
      "description": "CPI-U, 1982-84 = 100.",
      "format": "number"
    },
    "startMonth": {
      "label": "Start month",
      "description": "The month of the start CPI.",
      "format": "text"
    },
    "endMonth": {
      "label": "End month",
      "description": "The month of the end CPI.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "amount": 100,
      "from": "2000-01-01",
      "to": "2026-08-01"
    },
    "outputs": {
      "value": 198.4478672985782,
      "inflation": 98.44786729857819,
      "yearlyRate": 2.6116641743256563,
      "startCpi": 168.8,
      "endCpi": 334.98,
      "startMonth": "January 2000",
      "endMonth": "August 2026"
    },
    "text": "$100.00 in January 2000 has the same buying power as $198.45 in August 2026."
  },
  "examples": [
    {
      "given": {
        "amount": 100,
        "from": "2000-01-01",
        "to": "2026-01-01"
      },
      "expect": {
        "value": 192.68483412322274,
        "inflation": 92.68483412322274,
        "yearlyRate": 2.5547249917907244,
        "startCpi": 168.8,
        "endCpi": 325.252
      },
      "source": "BLS CPI-U (Jan 2000 168.8, Jan 2026 325.252); hand calculation in content.mdx",
      "tolerance": 1e-12
    },
    {
      "given": {
        "amount": 1000,
        "from": "2026-01-15",
        "to": "2000-01-31"
      },
      "expect": {
        "value": 518.9822045675353
      },
      "source": "BLS CPI-U; hand calculation in content.mdx",
      "tolerance": 1e-12
    },
    {
      "given": {
        "amount": 1,
        "from": "1913-01-01",
        "to": "2026-01-01"
      },
      "expect": {
        "value": 33.188979591836734,
        "startCpi": 9.8
      },
      "source": "BLS CPI-U (Jan 1913 9.8); hand calculation in content.mdx",
      "tolerance": 1e-12
    }
  ],
  "sources": [
    "U.S. Bureau of Labor Statistics, Consumer Price Index for All Urban Consumers (CPI-U), series CUUR0000SA0: https://data.bls.gov/timeseries/CUUR0000SA0",
    "U.S. Bureau of Labor Statistics, CPI Inflation Calculator (method): https://www.bls.gov/data/inflation_calculator.htm",
    "U.S. Bureau of Labor Statistics, CPI data during the 2025 lapse in appropriations (October 2025 not collected): https://www.bls.gov/cpi/"
  ],
  "related": [
    "cola",
    "compound-interest",
    "future-value"
  ],
  "changelog": []
}