# Inflation Time Machine

> What was money from one year worth in another? CPI-based, 20 countries, World Bank data. Convert an amount between years with the consumer price index (2010 = 100) published by the World Bank. Shows the equivalent value, cumulative inflation, average annual inflation and lost purchasing power, with a year-by-year table.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://inflationtimemachine.usefulweb.site/ (interactive tool at https://inflationtimemachine.usefulweb.site/tool)
- JSON API: POST https://inflationtimemachine.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://inflationtimemachine.usefulweb.site/api/v1/tool)
- OpenAPI: https://inflationtimemachine.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://inflationtimemachine.usefulweb.site/mcp - tool `inflation_time_machine`

## Inputs
- amount (number, required): Amount
- currency (text): Currency label - Label only. Use the currency of the chosen country; no conversion is done.
- fromYear (integer, required): From year
- toYear (integer, required): To year
- country (select): Country

## Method
- Data: World Bank WDI indicator FP.CPI.TOTL, consumer price index (2010 = 100), annual averages, snapshot stored with retrieval date.
- Equivalent value = amount × CPI(to year) ÷ CPI(from year).
- Cumulative inflation = (CPI(later) ÷ CPI(earlier) − 1) × 100.
- Average annual inflation (CAGR) = ((CPI(later) ÷ CPI(earlier))^(1 ÷ years) − 1) × 100.
- Purchasing power loss = (1 − CPI(earlier) ÷ CPI(later)) × 100: how much less the same nominal amount buys in the later year.
- Because CPI values are annual averages, results compare average price levels of whole years, not specific dates.