In digital electronics, a counter is a sequential circuit built from flip-flops and logic gates capable of storing and counting the impulses (often related to a clock signal), which it receives at the input intended for this purpose, and also acts as a frequency divider. Typically, the computation is done in the binary system, so the output will be a binary number or BCD (tens counter). A digital counter is a finite state machine.[1]​.

The maximum number of states a counter goes through is called the counter modulus (MOD Number). This number is determined by expression 2 where n indicates the number of bits of the counter. For example, a modulo 4 counter goes through 4 states, and would count from 0 to 3. If a counter with a modulus other than 2 is needed, a combinational circuit would have to be added.