Cost or book value is the initial outlay or price paid or payable for a particular security or debt investment. The preparer is expected to take reasonable measures in order to ensure that the amount reported in box 20 is correct. Do not enter the market value or the current price the asset was sold for in box 20. The investor needs this amount to calculate the adjusted cost base (ACB) of the security or debt investment and to track gains (or losses).

This amount may or may not reflect the investor's ACB for the purpose of determining his or her gain or loss from the disposition of the security. The investor should be aware that he or she may have to make adjustments to the amount indicated in box 20 at the time of determining and reporting his or her gain or loss from the disposition.