The RPI is the retail price index, which encompasses the cost of housing, home mortgage interest, and council tax. The RPI measures inflation by the retail price of items over time, and it is measured by combining price quotes on many of the same articles and an average day out over 12 months. The difference between the two the CPI, which is the consumer price index encompasses charges for doctors, drugs, transportation fees, fuels, clothing, and shelter.
The CPI is calculated by taking a bucket full of costs for them to get up one assumes up with us in the thing individual items as mentioned before, adding them up and averaging them. The CPI is calculated every month, and it tells us what the percentage is of inflation for that 30 days. However, it does not measure things like savings and investments, which is also paid out of your income. The difference between the CPI and the RPI would be what the consumer pays as opposed to what is charged for specific items.