Income elasticity of demand helps us to measure the health of an industry, future consumption patterns and economic reasoning behind investment decisions. The concept helps the managers to see the opportunities to maximize their profits.
When to increase or decrease your production?

The income elasticity of demand provides an answer to this question. We can find out the impact of increase or decrease in income of our targeted consumers on demand of our products. If we can catch up with economic cycles of a country and change in average income of the people, we can plan and make business decisions well in time to stay ahead of our competitors.
If we are selling necessities, the impact of an increase in income shall be slower or zero. However, in case of luxury products the rise in the income calls for an increase in our products to meet the rising demand.
The public managers can benefit from the concept of formulating public policies. In a study, Atakhanova and Howie (2007) calculated that incomeelasticity of demand for electricity in the residential sector is very low in comparison to demand in industrial and service sectors in Kazakhstan. They also discovered that overall income related elasticity of demand for electricity is also very low. They concluded that there would be no sociopolitical problem on electricity production if no further investment is made in the business. The public managers prefer to policies which bring investment in those products or services where income elasticity is higher.
You can find out incomeelasticity of demand by dividing percent change in demand of the quantity with percent change in income. You can use different formulas.
Suppose we have this data:
Q1 = Initial quantity
Q2 = Changed quantity
Y1 = Initial Income
Y2 = Changed income
You can measure percentage change in Quantity by these calculations:
= {(Q1Q2)/[1/2(Q1+Q2)]} x 100
You can measure percentage change in income as under:
= {(Y1Y2)/[1/2(Y1+Y2)]} x 100
By combining these two we find this simple formula:
Here "Ey" is an expression of income elasticity of demand.
Another simple formula to calculate elasticity of demand is:
Suppose we are in the housing business. Due to overall economic deterioration, the income of our targeted consumers falls by 6% annually. It leads them to purchase 5 million fewer houses and demand falls from 25 to 20 million. What would be income elasticity of demand?
We already have 6% drop in income. To calculate the percent change in quantity we use this formula:
= {(Q1Q2)/[1/2(Q1+Q2)]} x 100
= {(2520)/[1/2(25+20)]} x 100
= (5/22.5)x100
= 22%
Ey= 22/6 = 3.66
2 Suppose you are selling 1000 items of a product having an elasticity of demand 1.2. You see an increase of 20% in the annual income of the people of that particular income group. How much production of that product shall maximize your profits by coming up to the increased demand.
How much would be the change in the demanded quantity of the product?
First, we shall find out the percent change in quantity by multiplying elasticity with percent increase in income.
= 1.2x20 =24%
There will be 24% increase in demand for the product which means we will need to produce 240 more items to meet this demand and to maximize our profits.
3 Suppose income of every Pakistani increases by 200%. Everyone will have more money so demand for many inferior products shall fall. Suppose demand for low quality wine drops by 10%. We can calculate it in a straightforward way as:
10%/200%= 0.05
It is an example of negative elasticity of demand.
In United States following products have different income elasticity of demand:
Product 
Income Elasticity 
Elasticity Level 
Oversea Travels 
3.08 
Elastic 
Motion Pictures 
3.41 
Elastic 
Housing Services 
2.45 
Elastic 
Electricity 
1.94 
Elastic 
Restaurant Food 
1.61 
Elastic 
Mass Transport 
1.38 
Elastic 
Petrol and Gasoline 
1.36 
Elastic 
Hair Cuttings 
1.36 
Elastic 
Cars 
1.07 
Elastic 
Dentist’ Services 
1.00 
Unitary Elastic 
Shoes and other footwear 
0.94 
inelastic 
Tobacco 
0.86 
inelastic 
Alcohol 
0.62 
inelastic 
Furniture 
0.53 
inelastic 
Clothing 
0.51 
inelastic 
Newspapers 
0.38 
inelastic 
Phone 
0.32 
inelastic 
Food 
0.14 
inelastic 
Sources: H.S. Houthakker and Lester D. Taylor, “Consumer Demand in the United States,” and Henri Theil, ChinesFan Chung and James L. Scaler, Jr., “Advances in Econometrics”
In this table, inelastic does not mean entirely inelastic which equals to zero. It is above zero but relatively inelastic. According to statistician Ernst Engel (18211896) demand for low necessities like food also changes but at snail's pace.
More on Income Elasticity of Demand
Measurement of Demand Elasticity
Perfect Price Elasticity of Supply
Relative Elasticities and Inelasticity of Supply