See also: Time control and Byoyomi
A game of Go may be timed using a game clock. Formal time controls were introduced into the professional game during the 1920s and were controversial.? Adjournments and sealed moves began to be regulated in the 1930s. Go tournaments use a number of different time control systems. All common systems envisage a single main period of time for each player for the game, but they vary on the protocols for continuation (in overtime) after a player has finished that time allowance. The most widely used time control system is the so called byoyomi system. The top professional Go matches have timekeepers so that the players do not have to press their own clocks.

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Two widely used variants of the byoyomi system are:

- Standard byoyomi: After the main time is depleted, a player has a certain number of time periods (typically around thirty seconds). After each move, the number of full time periods that the player took (possibly zero) is subtracted. For example, if a player has three thirty-second time periods and takes thirty or more (but less than sixty) seconds to make a move, they lose one time period. With 60?89 seconds, they lose two time periods, and so on. If, however, they take less than thirty seconds, the timer simply resets without subtracting any periods. Using up the last period means that the player has lost on time.
- Canadian byoyomi: After using all of their main time, a player must make a certain number of moves within a certain period of time, such as twenty moves within five minutes. If the time period expires without the required number of stones having been played, then the player has lost on time.