Inflation headlines move markets and kitchen-table budgets, yet the underlying charts are easy to misread. This page is a calm walkthrough of how to open a consumer price series on FRED (US) or the ONS (UK), what year-on-year versus month-on-month means, and how “core” measures differ from headline prints. It is original guidance for literacy — not a forecast and not investment advice.

What CPI is trying to do

A consumer price index estimates how the cost of a representative basket of goods and services changes over time. Statistical agencies survey prices, weight items by spending patterns, and publish index levels and growth rates. The index level is a constructed number (often rebased to 100 in a reference period). The growth rate — inflation — is what most readers want.

US readers usually start with the BLS CPI; many macro watchers also track the Fed’s preferred PCE price index from the BEA. UK readers start with ONS CPI and CPIH (CPI including owner-occupiers’ housing costs). Headline measures include food and energy; core or underlying measures exclude some volatile components to highlight persistence.

Open the series (US via FRED)

  1. Go to FRED series CPIAUCSL (CPI for All Urban Consumers, seasonally adjusted index).
  2. Look at the chart of the index level first — it should drift upward over decades in an inflationary economy.
  3. Use FRED’s units menu to switch to Percent Change from Year Ago for a standard year-on-year inflation rate.
  4. Compare with a core variant such as CPILFESL (less food and energy) when you want to abstract from petrol and grocery spikes.
  5. Note the observation date and revision policy in the series notes — always read the footnotes once.

Open the series (UK via ONS)

  1. Visit the ONS inflation and price indices hub.
  2. Open the latest CPI or CPIH bulletin and find the 12-month (year-on-year) growth rate table.
  3. Check whether the discussion emphasises CPI (BoE target definition) or CPIH (broader household costs).
  4. Scan the contributions chart: energy, food, goods, and services often drive the monthly narrative in different proportions.
  5. For long charts, ONS time series and tools linked from the bulletin let you download history rather than copying a single headline number.

Year-on-year versus month-on-month

Year-on-year compares this month’s index with the same month a year earlier. It smooths some noise and matches how many wage negotiations talk about inflation. Month-on-month shows the latest impulse; annualised forms of that impulse are sometimes used in commentary but can be volatile. Base effects matter: a big drop a year ago can mechanically raise today’s year-on-year rate even if recent months are calm.

Example (illustrative)

If the index is 120 today and was 115 a year ago, year-on-year inflation is 120/115 − 1 ≈ 4.3%. That arithmetic is an illustration — pull the live index from FRED or ONS before quoting a rate.

Seasonal adjustment and housing

Seasonally adjusted series strip typical calendar patterns (sales, travel seasons). Prefer seasonally adjusted month-on-month reads for near-term momentum; year-on-year rates already compare like months. Housing measurement differs: US CPI shelter components behave differently from UK CPIH owner-occupier costs. Comparing “US vs UK inflation” without checking concepts is a common mistake.

How this connects across the site

Once you can read CPI charts, revisit inflation, real interest rates, and the inflation adjuster. Country hubs: United States, United Kingdom. Glossary: CPI, disinflation.

Building a simple personal checklist

Before sharing an inflation number, confirm: (1) which index (CPI, CPIH, PCE, core variant); (2) which growth rate (12-month, monthly, or trimmed-mean style measures); (3) the release date and whether it is seasonally adjusted; (4) whether the claim mixes levels with rates. That checklist prevents most viral misreads.

For classroom or study use, download a long history once, compute a year-on-year series yourself, and compare to the published rate. Doing the arithmetic once builds intuition that no headline can replace. Keep the disclaimer in mind: literacy is the goal, not trading signals.

Where to go next on this site

After CPI, many readers graduate to unemployment rates and real GDP. The same habits apply: know the agency, the seasonal adjustment, and the growth convention. Country snapshots for the US and UK list starting portals. Long-form context lives under explainers, including recession definitions and real interest rates.

Common chart traps

Truncated vertical axes can make small inflation changes look dramatic. Mixing index levels with percent changes on one axis confuses readers. Comparing a non-seasonally adjusted monthly blip with a year-on-year target is a category error. When in doubt, screenshot the series settings (units, frequency, seasonal adjustment) alongside the chart.

Sources