A Commission is generally a service charge that is paid to a broker based on the performance and the value of trades executed. When an investor is working with a broker or real estate agent to purchase commercial or residential property, the amount to be paid in Commission will need to be discussed. Commissions are paid by the investor as remuneration to the broker for the successful completion of a real estate sale. Commissions should be decided upon and written in a contract before any work is done on behalf of the investor. Both the investor and the broker should read and sign the contract. When a transaction involving a real estate investment is made, it is customary for the broker to charge a Commission. The Commission is generally calculated as a percentage of the final cost of the property. Commissions are negotiable, but are generally based on the monetary performance of the property and the value of the property itself. All Commissions are contingent upon the final successful brokerage of the property and are paid at closing.