Tax withholdings are applied to the coupons and implied yields of assets such as commercial paper. They constitute a reduction in the coupon or implied yield.
The returns obtained from coupons are considered investment income and are included as taxable income (IRPF). These instruments are therefore liable to the same tax withholding as any other income during the tax year. However, the difference between the redemption value of a bond (normally the face value) and the price paid for the bond is considered an increase or decrease in equity.