Share Cost Base is the official term for a method of calculating how much tax an investor owes on capital gains. In simple terms, it involves multiplying the number of shares you own by their cost and subtracting any expenses related to buying or selling those shares. This is then used to calculate your capital gains or losses when selling stocks that have gone up in value. The share cost base is an important tool for managing tax obligations while investing, and should be kept up-to-date as investments are made or sold.