Time Systems limit the period of time available to each player.
Typically there is a device for that purpose, called clock, which at least shows the remaining time for each player and who's turn it is.
Players hit it alternately to signal turn completion, stopping their side of the clock and resuming the other. Depending on the time system, this may trigger further actions. As soon a player exhausts all time, the player loses on time (no matter if the turn was complete or not).
Common time systems for Go are
- Absolute Timing (Sudden Death)
- Absolute Timing plus
- Absolute plus Japanese Timing
- Japanese Timing (Japanese title matches)
- Per Move plus Overtime
- Ing Timing (Ing Time Purchasing System)
- Capped Fischer Timing (Used by 3 Turn Based Go Servers)
Less common for Go are
- Bronstein Timing (bonus after each move, but spilling)
- Fischer Timing (bonus after each move)
- Round Down Timing (Canadian and Japanese in one)
- Steady Average Timing (Milton Keynes, N moves in each period of time)
- Total Average Timing (non-spilling variant of Canadian, generalization of Fischer Timing; add period after each N moves)
- Hourglass Timing (crazy time system)
- Cell Phone Timing (humor)
- Hayashi Timing - no loss on time, as you simply lose your turn
Turn based play fundamentally requires to handle time in a different way: although many of the timing systems above are usually available on such servers, these timing systems are less suited, in favour of:
Also, is there a way to play games without a game clock (eg with a normal clock, or countdown timer as found on watches and cell phones)? Is it possible to organise a tournament without game clocks (i.e. with a gong)?
- BGA Tournament Rules
- Sportsmanship (Chapter 7: The Clock)
- Allotting Extra Time
- Not Using Your Time
- Wasting Time in a Lost Game
- Use Your Opponents Time Too
- Timing Systems - Redux
- Common Clock rules
- Ancient Time Systems
 Time may also include other things, like number of lifes. For instance, eight hours Japanese Timing in periods of one minute is like having a single one-minute period backed up by 479 lifes.
 With no timekeeper, a move is complete when the clock is hit.
- However, with a timekeeper, the move should be complete when the stone was released (or "pass" uttered), but I'm not sure how it really is. Someone?
- I'd say that if at the moment of appeal (and stopping the clock) several players are without time, the one who's last move is oldest has lost -- but there certainly are other ideas . . .
 Time systems can be combined. T1 plus T2 means that the player who would have lost by time under T1 instead enters T2 and continues. This option is like being backed up by one life.