How Does a Chess Clock Work? A Plain-English Guide
By the PomoTimer team. Last updated .
A chess clock is two linked timers, one for each player, and only one of them runs at a time. When you finish your move, you press your button: your clock stops and your opponent's starts. Each player has their own bank of time for the game, and if your clock runs out before the game ends, you normally lose on time.
What is the clock used in chess called?
It's simply called a chess clock, or more generally a game clock, since the same device is used for Go, Scrabble and other two-player games. Club players also call it a "chess timer." It's there to make sure neither player can stall forever and that both get a fair, equal share of the thinking time.
Before clocks were common, some 19th-century matches were timed with sand glasses, the same idea as a modern sand timer. Mechanical chess clocks, with two clock faces and two buttons on top, became the standard for tournaments in the late 1800s, and digital clocks largely replaced them over the last few decades.
How a chess clock works, step by step
- Set the time. Both clocks are set to the agreed time control, for example 10 minutes each.
- Start White's clock. At the start of the game, White's time begins to run (in many settings Black presses the clock to start it).
- Move, then press. White makes a move and presses their button. White's clock stops and Black's starts.
- Repeat. Players alternate: move, press, move, press. Only the player whose turn it is loses time.
- Game ends by checkmate, resignation, a draw, or one player running out of time.
Two habits matter in serious play. Press the clock with the same hand you moved with, which is the rule under FIDE (the international chess federation) and keeps play fair. And press only after your move is complete; the move isn't finished until you've let go of the piece and stopped your clock.
What happens when the flag falls?
On a mechanical clock, a small red "flag" is lifted by the minute hand as it approaches the hour mark and drops when time is up. "Flag fall" is still the term for running out of time, even though digital clocks just show a flag symbol or 0:00.
Under standard rules, a player whose flag falls loses on time. The main exception: if the opponent has no possible way to checkmate (for example, they have only a king left), the game is a draw instead. In casual games, it's usually up to the opponent to notice and point out that time has run out.
Chess time controls, increment and delay
A time control tells you how much time each player gets. The simplest is sudden death: one bank of time for the whole game, like "10 minutes." Games are grouped by speed into bullet, blitz, rapid and classical; our online chess clock page has a table of the usual ranges.
Many time controls also add a little time per move, which keeps games from being decided purely by who can move fastest at the end:
| Method | How it works | Example notation |
|---|---|---|
| Sudden death | One fixed amount of time for the whole game, nothing added | 10 min, or "10+0" |
| Fischer increment | A set number of seconds is added after each move; unused time can build up | "3+2" = 3 minutes plus 2 seconds per move |
| Simple delay (US delay) | Your clock waits a few seconds before it starts counting down each move | US tournament listings often show it as "G/90;d5" |
| Bronstein delay | After each move, you get back the time you used, up to the delay amount | Same effect as simple delay, shown differently on the clock |
The key difference: with an increment, a fast player can end up with more time than they started with. With either kind of delay, you can never gain time; a quick move just costs you nothing. Mechanical clocks can't do increment or delay, which is one reason digital clocks took over in tournaments.
How to use a chess clock with PomoTimer
The PomoTimer chess clock turns a phone, tablet or laptop into a two-player clock for sudden-death games:
- Click Set Time and enter the minutes each player gets, such as 5 for blitz or 15 for a relaxed rapid game.
- Place the device beside the board, within reach of both players.
- Press Start to begin Player 1's clock, then press the switch button after every move.
- Use Pause if you need to stop both clocks; an alarm sounds when a player reaches zero.
Be aware of its limits: both players always get the same starting time, and it has no increment or delay, so you can't play "3+2" or "G/30;d5" on it. For tournament practice with increment, use a dedicated digital chess clock. For a single shared countdown, such as a time limit for a whole puzzle session, use the countdown timer.
Frequently asked questions
Which side of the board does the clock go on?
Put it to one side of the board, between the players, so both can reach it. In tournaments the arbiter or local rules decide; at home, agree on a side before you start.
How much time should beginners use?
Fifteen to thirty minutes each is a comfortable start. Very short games mostly train fast reflexes; longer ones give you time to think through your moves.
What if a player forgets to press the clock?
Their own time keeps running, which is their problem, not their opponent's. In casual games, players often agree to a friendly reminder.