A half adder is a type of adder, an electronic circuit that performs the addition of numbers. The half adder is able to add two single binary digits and provide the output plus a carry value. It has two inputs, called A and B, and two outputs S (sum) and C (carry). The common representation uses a XOR logic gate and an AND logic gate.

A half adder is used to add two single-digit binary numbers and results into a two-digit output. It is named as such because putting two half adders together with the use of an OR gate results in a full adder. In other words, it only does half the work of a full adder.

The adder works by combining the operations of basic logic gates, with the simplest form using only a XOR and an AND gate. This can also be converted into a circuit that only has AND, OR and NOT gates. This is especially useful since these three simpler logic gate ICs (integrated circuits) are more common and available than the XOR IC, though this might result in a bigger circuit since three different chips are used instead of just one.