This is the difference between what you bought an investment for and what you sell if for. If you buy 100 shares of a stock at $10 a share (spending $1,000) and sell your shares later for $25 a share ($2,500), you have a capital gain of $1,500. A loss occurs when you sell for less than you paid. So, if you sell this stock for $5 instead ($500), you have a capital loss of $500).