Inflation Formula | Calculator (Example with Excel Template)

Inflation Formula (Table of Contents)

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What is the Inflation Formula?

The term “Inflation” refers to the increase in prices of commonly used goods and services in an economy during a certain given period, usually a year. In other words, this economic metric compares the prices of goods and services across different periods and ultimately assesses its impact on the purchasing power of the population.

The formula for inflation is expressed as a difference between consumer price index (CPI) of the current year and that of the previous year which is then divided by the CPI of the previous year and expressed in terms of percentage. Mathematically, it is represented as,

Inflation = (CPI _x+1 – CPI _x) / CPI _x

Where,

CPI _x+1: CPI of Current Year
CPI _x: CPI of Previous Year

Example of Inflation Formula (With Excel Template)

Let’s take an example to understand the calculation of Inflation in a better manner.

You can download this Inflation Formula Excel Template here – Inflation Formula Excel Template

Inflation Formula – Example #1

Let us take the simple example of a commodity with CPI of 150 last year which has soared up to 158 in the current year. Calculate the rate of inflation of the commodity in the current year based on the given information.

Solution:

Inflation is calculated using the formula given below

Inflation = (CPI _x+1 – CPI _x) / CPI _x

Inflation = (158 – 150) / 150
Inflation = 5.33%

Therefore, the commodity’s rate of inflation was 5.33% in the current year.

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Inflation Formula – Example #2

Let us take the example of Dylan who is an economist and wishes to compute the inflation rate in his state. He has created a CPI basket that includes food, cloth, fuel and education and has considered 2010 as the base year. According to Dylan, average consumers in his state spend 30% of their total budget on food, 24% on cloth, 28% on fuel and 18% on education. Dylan gathered the following information pertaining to prices in the state. Calculate the CPI in the year 2018 and 2019, then calculate the inflation in 2019.

Solution:

Value of basket is calculated as

CPI is calculated using the formula given below

CPI = ∑ Weightage of Item * Price of Item / ∑ Weightage of Item * Price of Item in 2010

For Year 2018

CPI = (30% * $47 + 24% * $58 + 28% * $40 + 18% * $39) / (30% * $35 + 24% * $52 + 28% * $38 + 18% * $27) * 100
CPI = 120.17

For Year 2019

CPI = (30% * $50 + 24% * $60 + 28% * $41 + 18% * $40) / (30% * $35 + 24% * $52 + 28% * $38 + 18% * $27) * 100
CPI = 124.95

Inflation is calculated using the formula given below

Inflation = (CPI ₂₀₁₉ – CPI ₂₀₁₈) / CPI ₂₀₁₈

Inflation = (124.95 – 120.17) / 120.17
Inflation = 3.98%

Therefore, Dylan found out that the rate of inflation for the year 2019 stood at 3.98%.

Explanation

The formula for Inflation can be calculated by using the following steps:

Step 1: Firstly, in case you wish to create a customized CPI basket, then determine what are the commonly used goods and services that you want to include in the basket. The CPI of the basket is the weighted average price. Otherwise, general CPI data is available at government websites.

Step 2: Next, determine which year you want to consider as the base year. In the base year, the CPI of the above-selected basket will be considered as 100 and then in the following years, the price of the basket will express relative to the base year.

Step 3: Next, determine the CPI of the basket in the current year which is denoted by CPI _x+1.

Step 4: Next, determine the CPI of the basket in the previous year which is denoted by CPI _x.

Step 5: Finally, the formula for inflation can be derived by deducting CPI of the previous year (step 4) from CPI of the current year (step 3) which is then divided by the CPI of the previous year and expressed in terms of percentage as shown below.

Inflation = (CPI _x+1 – CPI _x) / CPI _x

Relevance and Use of Inflation Formula

The concept of inflation is very important and interesting as it tells you how much of your purchasing power has gone down in each period due to the increase in the prices of the commonly used goods and services. The inflation is computed using the CPI which is another important economic indicator. Inflation can significantly and equally influence the cost structure of businesses and budgetary plans of the government.

Some of the causes of inflation are natural disasters and government regulations. For instance, Hurricane Katrina created mayhem in the US in 2005 as the storm ruined oil refineries resulting in a surge in gas prices. On the other hand, in order to moderate the consumption of cigarettes and alcohol government at times imposes higher taxes on these items resulting in increased price and hence inflation.