The radix complement of n digit number y in radix b is defined to be 
. Therefore, the radix complement of a number y is the number that when added to y causes the sum to “roll over” to n+1 digits.
The radix complement of a decimal number is known as the ten’s complement while the radix complement of a binary number is called the two’s complement.
The easiest way to calculate the radix complement of y is to add 1 to the diminished radix complement of y, 
, so the radix complement is 
.