Methodology & Data Sources
How we calculate historical purchasing power and where our data comes from.
United States Data (USD)
All United States inflation calculations are based on the Consumer Price Index for All Urban Consumers (CPI-U). This data is published monthly by the U.S. Bureau of Labor Statistics (BLS).
We use the annual average CPI value to calculate year-over-year changes. This ensures that seasonal volatility is smoothed out, providing a more accurate representation of annual purchasing power.
United Kingdom Data (GBP)
United Kingdom inflation data is sourced from the Office for National Statistics (ONS).
Our calculations utilize the composite price index, which stitches together historical Retail Price Index (RPI) data with modern Consumer Prices Index (CPI) data to provide a continuous, historically accurate measure of inflation spanning several decades.
The Calculation Formula
To determine the adjusted value of money between two different years, we use the standard inflation formula:
For example, to find the value of $100 from 1990 in 2026, we divide the 2026 CPI by the 1990 CPI, and multiply the result by 100.
Commodity Pricing ("What it Bought")
The comparative prices for goods like gasoline/petrol and movie tickets are aggregated from historical retail reports, including the U.S. Energy Information Administration (EIA) and the UK Department for Energy Security and Net Zero. These figures represent national averages for the given year and are meant for illustrative purposes.