Methodology

The data

The calculator uses the Consumer price index (2010 = 100) series (indicator FP.CPI.TOTL) from World Bank Open Data. The World Bank compiles this from the official CPI published by each country’s national statistics agency, which makes it the most consistent way to cover many countries with one method.

• Coverage: 192 countries with at least two years of data.
• Frequency: annual. Each value is the average index across that calendar year.
• Base: the series is published with 2010 = 100. The base cancels out of every formula below.
• Snapshot taken: 2026-09-14.

The dataset is baked into the site at build time, so results do not depend on a live API and the calculator keeps working offline once the page has loaded.

The formulas

Inflation-adjusted value

The core calculation is a ratio of two index values:

adjusted = amount × (CPI[end year] ÷ CPI[start year])

Because both terms are drawn from the same series, whatever year the index is anchored to divides out. An index of 60 → 120 and an index of 100 → 200 give exactly the same answer.

Cumulative inflation

cumulative % = (CPI[end] ÷ CPI[start] − 1) × 100

The total change in the price level across the whole period.

Average annual inflation

annual % = ((CPI[end] ÷ CPI[start]) ^ (1 ÷ years) − 1) × 100

This is the geometric mean — the constant rate that compounds to the same total. It is deliberately not the arithmetic average of the yearly rates, which would overstate the result.

Purchasing power

power % = (CPI[start] ÷ CPI[end]) × 100

How much of the original buying power survives. It is the reciprocal of the adjustment ratio, so 250% cumulative inflation leaves about 28.6% of the purchasing power.

Future value projection

future = amount × (1 + rate) ^ years

Standard compounding at a rate you supply. This is an assumption, not a measurement, and is pre-filled with the country’s long-run average purely as a starting point.

Limitations

• Annual, not monthly. Results reflect calendar-year averages. A national calculator comparing, say, June to June will give a slightly different figure.
• CPI is an average basket. It measures a representative household’s spending. If your own spending is weighted towards housing, education or healthcare, your personal inflation rate may be considerably higher.
• Series breaks and revisions. Countries periodically re-base or revise their index, and currency redenominations sit inside some long series. Very long spans in high-inflation economies should be read as indicative.
• Gaps. Some countries have missing years. The year menus only offer years with a published figure, and gap years are skipped in the year-by-year table.
• Not financial advice. This is a reference tool for understanding price changes, not a basis for investment decisions.

Rebuilding the dataset

The dataset is regenerated by running node scripts/fetch-cpi.mjs, which pulls the current series from the World Bank API and rewrites the bundled data file. Re-running it and rebuilding the site is all that is needed to pick up a new year of data.