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 .