When we talk about inflation in the UK, two important ideas come up: CPI and RPI.

Both of these measure inflation, but they do it in different ways.

CPI (Consumer Price Index):

1. What it Measures: CPI is the main way we look at inflation. It looks at a wide range of items and services people buy.

2. How it Works: It uses a special method called a geometric mean to figure out price changes. This usually leads to a lower inflation rate.

3. What it Leaves Out: CPI does not include some costs like mortgage interest payments and certain housing expenses.

RPI (Retail Price Index):

1. What it Measures: RPI is an older method and includes more items, making it a bit broader than CPI.

2. How it Works: RPI uses a different method, called an arithmetic mean, which often gives a higher inflation number.

3. What it Includes: RPI includes housing costs, like mortgage interests, so it can be more helpful for homeowners.

In simple terms, if you want to see how general prices are changing for everyday things, you will probably look at CPI. But if you're interested in how inflation affects your mortgage, RPI is a better choice.

Both are helpful, just for different situations!