How to Calculate Net Income Based on Stock Price

Visit any financial website that gives stock information and find a company’s P/E ratio, price per share and number of shares outstanding, which is information that a financial website provides for all public companies. For example, assume a company’s P/E ratio is 12, its price per share is $20 and it has 1 million shares outstanding.
Substitute the values into the P/E ratio formula: P/E ratio = price per share/(net income/shares outstanding). In this example, substitute the values to get 12 = $20/(net income/1 million).
Multiply both sides of the equation by the right side’s denominator. In this example, multiply both sides by (net income/1 million) to get 12 x (net income/1 million) = $20.
Divide the company’s P/E ratio by its total shares outstanding. In this example, divide 12 by 1 million to get 0.000012. This leaves 0.000012 x net income = $20.
Divide the company’s stock price per share by your result to calculate its net income over the past 12 months. In this example, divide $20 by 0.000012 to get approximately $1.7 million in net income over the past 12 months.

How to Calculate Fair Value for a Stock

Calculate the P/E ratio. The formula used to calculate the P/E ratio is 'current stock price per share' / ' current earnings per share.'
Compare the P/E ratio for your company with other companies in the same industry. For instance, if you want to find the fair value for a bank, you must compare the P/E ratio to other P/E ratios in the banking industry.
Interpret the meaning of the P/E ratio. A high P/E ratio means the company is overvalued and a low P/E ratio means the company is undervalued. For instance, if I own a company with a P/E ratio of 5 when the average P/E ratio for companies in the same industry is 3, I know that my stock is overvalued (expensive).
Adjust the stock price down to the average P/E ratio for the industry. If the average P/E ratio is 3, and the P/E ratio on my stock is 5 (current price $10 / earnings per share $2), then I can use the P/E equation to find what the stock price would need to be in order to have a P/E ratio of 3. The equation is: New P/E ratio x Earnings per share. The answer is 3 x $2 or $6. The fair market value for this stock is $6, not $10.