Obtain a company's balance sheets for two consecutive accounting periods from its 10-Q quarterly filings or from its 10-K annual filings. You can get these filings from the U.S. Securities and Exchange Commission's EDGAR online database or from the investor relations section of the company's website.
Find the amount of the company's total paid-in capital, listed in the Stockholders' Equity section of the most recent balance sheet. For example, assume the company's most recent balance sheet shows $500,000 in total paid-in capital.
Identify the amount of total paid-in capital, listed on the previous period's balance sheet. In this example, assume the previous period's balance sheet shows $400,000 in total paid-in capital.
Subtract the previous period's total paid-in capital from the most recent period's total paid-in capital to calculate the additional investment from stockholders. In this example, subtract $400,000 from $500,000 to get $100,000 in additional investment.