Methodology

Where the figures come from

Every series is the headline consumer price index published by the country's own statistics office, rebased so that 2015 = 100 and any two dates can be compared directly. UK figures come from the ONS, US figures from the Bureau of Labor Statistics, EU members from Eurostat and the OECD, and the rest from OECD and IMF republications of each national release.

Where a country publishes more than one measure, the one used is the measure that country headlines, so a figure here matches the one its own office quotes. The UK is the exception a reader is most likely to notice: both CPI and RPI are offered, because both are in common use there.

What each figure means

Current inflation is the change in the index over twelve months, comparing the latest reading with the same month a year earlier. It is not the change since the start of the year.

Inflation in a year, in the year-by-year tables, is that year's average price level against the previous year's average. This is the definition national offices and most reference works use, so the figures match the ones quoted elsewhere: it gives the USA 11.0% for 1974 and 13.5% for 1980. Measuring January to January or December to December gives noticeably different answers, and would put this site at odds with every other source.

What a sum is worth today takes the amount in January of the year named and scales it by the ratio of the latest index to that month's. It is the change in the general price level, not the price of any particular thing.

What is left out

A year needs a complete set of readings on both sides to have an average, so a series that opens partway through a year has no rate for that year or the one after it, and a year still running has none until it ends. Those years are omitted rather than estimated from the months that exist.

Where readings stop and resume — Belgium's records break for the occupation and pick up again in 1947 — the missing years are absent from the tables and the page says the list is not continuous.

Comparing one country with another

The comparison tables rank countries by their own latest published figure, which means the dates differ: offices publish on different schedules, and each row says which month or quarter it is on.

Baskets and methods differ between countries too. Two national measures are not a perfect like-for-like comparison, and the tables say so where they appear. What they are good for is the order of magnitude and the direction of travel, which is what the ranking shows.

Accuracy

The build checks itself. Figures quoted in the written histories are cross-checked against the series they sit on, superlatives are verified against the whole series rather than the part before them, and the build fails loudly rather than publishing a claim it cannot support.

None of that makes the site infallible. If a figure here disagrees with the office that published it, the office is right and this is a bug worth reporting.