To calculate the two's complement, first calculate the ones' complement and then add 1. This is equivalent to inverting all the digits and adding 1. For example, the decimal number 125 is 01111101. To express –125 in two's complement, first invert the digits of 01111101 to get 10000010, and then add 1 to get 10000011. You can verify the result using the preceding table. To go backward, do the same thing—invert all the bits and add 1.