Chess Clock Timer

Time control preset:

Choose a starting time control, then adjust the mode or bonus seconds if needed.

Clock mode:

Use sudden death, Fischer increment, Bronstein delay, or simple delay.

Starting time:

Set the base clock loaded for each side.

min s

{{ timingBonusLabel }}:

White player:

Keep this short for a readable over-the-board display.

Black player:

Keep this short for a readable over-the-board display.

First side to move:

White normally moves first; switch for setup drills or odds games.

{{ error }}

Low-time warning:

Use 0 to disable low-time pressure badges.

Boundary tones:

Leave off for silent tournament-room use.

Tone volume: {{ params.soundVolume }}%

Set 0-100 percent.

Side	Player	Clock	Moves	Spent	Status	Copy
{{ row.sideLabel }}	{{ row.player }}	{{ row.clock }}	{{ row.moves }}	{{ row.spent }}	{{ row.status }}

Setting	Value	Detail	Copy
{{ row.setting }}	{{ row.value }}	{{ row.detail }}

#	Time	Event	Side	White	Black	Detail	Copy
{{ row.number }}	{{ row.time }}	{{ row.event }}	{{ row.side }}	{{ row.whiteClock }}	{{ row.blackClock }}	{{ row.detail }}

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A chess clock divides thinking time between two players while making sure only the player to move is spending time. That simple rule changes the feel of a game. A quiet endgame with a large clock margin rewards calculation, while a scramble under 30 seconds rewards clear moves and clean clock handling.

Time controls are usually written as a base time plus a per-move bonus, such as 5+3. The first number is the starting minutes for each player. The second number is the number of seconds attached to each move, but that bonus can behave differently depending on the clock mode. Fischer increment can add bankable time, Bronstein delay can refund used time up to a limit, and simple delay waits before the main clock starts falling.

Simplified chess clock diagram showing white and black clocks, the turn switch action, and the three bonus modes: Fischer increment, Bronstein refund, and simple delay.

Clock timing is useful for friendly games, club skittles, training drills, and quick adjudication of who still has time on the board. It is not a substitute for tournament equipment, tournament pairing rules, or an arbiter's decision. For casual use, the important habit is to agree on the exact mode before the first move and then press the clock consistently after each move.

A flag shows that a player's allotted time has expired. In a rated or formal game, what happens after a flag depends on the rule set, the position, and the claim procedure. For practice, the clock can still teach the same practical lesson: choose a time control that matches the game you want to play, then treat the clock setting as part of the game agreement.

Technical Details:

A chess clock has two displays connected so only one display runs at a time. When the player to move completes a move and presses the clock, that player's display stops and the opponent's display starts. The time between making the move and pressing the clock belongs to the player who just moved, so late presses matter even when the board move itself was quick.

The time-control mode decides how the per-move bonus interacts with the main clock. A sudden countdown charges every active second immediately. Fischer increment changes the remaining time after a completed move. Delay modes protect a fixed amount of time on each move, but they do not let unused delay accumulate as extra main time.

Rule Core:

Clock mode rules used by the chess clock timer
Mode	During the move	After the clock is pressed	Can unused bonus be banked?
`Simple countdown`	The active clock decreases immediately.	No bonus is added.	No.
`Fischer increment`	The active clock decreases while the player thinks.	The selected increment is added to that player's remaining time.	Yes, if the move used less time than the increment added.
`Bronstein delay`	The active clock decreases while the player thinks.	Spent time is refunded up to the delay amount, capped at the pre-move clock value.	No. The clock cannot rise above the time shown at the start of that move.
`Simple delay`	Main time waits until the delay expires, then begins decreasing.	No refund is needed because protected delay time was not charged.	No.

The running state is event based. The ledger records setup, start, pause, turn switch, reset, and flag events with the white and black times shown at that moment. The balance chart uses those recorded events, so it is a clock-history chart rather than a second-by-second recording of every tick.

Bounds and Status Rules:

Input bounds and status rules for the chess clock timer
Setting or output	Rule	Practical effect
`Starting time`	0 to 600 minutes plus 0 to 59 seconds, with total time required to be above 0 seconds.	A `0:00` setup stops with `Starting time must be above 0 seconds.`
`Increment`, `Delay refund`, or `Delay`	0 to 120 seconds; disabled for `Simple countdown`.	The same numeric field changes meaning when the clock mode changes.
`Low-time warning`	0 to 600 seconds; 0 disables the warning.	A side at or below the threshold is marked `Low time` and the summary badge changes to a pressure state.
`Flag`	A side flags when its active clock reaches 0.	The clock stops, the flagged side is named, and a flag event is added to the ledger.
`Move Ledger`	The newest 250 events are kept.	Very long practice sessions keep a recent audit trail without growing indefinitely.

Displayed clocks round up for normal display, and the active clock shows tenths only when it is running below 10 seconds. That keeps the main display readable during most of the game while still giving more precision when a flag is near.

Everyday Use & Decision Guide:

For a normal first pass, choose the closest Time control preset and then check the Clock mode. Blitz 5+3 is a balanced practice default because it gives both players five minutes and restores three seconds after each completed move. Use Bullet 1+0 only when both players are comfortable with fast play and quick clock handling.

Switch to Custom when you need a club-specific setting, a drill where Black moves first, or a delay mode instead of increment. Agree on the meaning of the bonus before the game starts. A setting labeled 5+3 can feel very different in Fischer mode than in Bronstein or simple delay mode.

Set White player and Black player before starting if you plan to copy the ledger or export a table later.
Leave First side to move on White for ordinary chess, and change it only for setup drills, odds games, or variants.
Use Low-time warning as a training cue. The default 30 seconds is useful for blitz and rapid practice, but it can be too noisy for a one-minute bullet game.
Keep Boundary tones off in shared rooms unless both players want audible switch, pause, and flag cues.
Use Current Clocks for the live state, Time Control Brief for setup confirmation, and Move Ledger when a pause, reset, or flag needs a quick audit trail.

Do not treat the balance chart as proof of every second spent. It shows clock values at recorded events, which is enough to review switches and flags but not enough to reconstruct every hesitation between presses. For a dispute, the visible clock state and the agreed rules still matter more than a chart shape.

Before starting a serious game, run one test switch. The summary should move from Chess clock ready to Chess clock running, the active side should change after Switch turn, and the Time Control Brief should match the agreed preset and mode.

Step-by-Step Guide:

Set the time control first, then start the clock and use the result tabs to confirm what happened.

Choose Time control preset. If none matches, select Custom and set Starting time in minutes and seconds.
Choose Clock mode. For Fischer increment, set the number of seconds added after a completed move. For Bronstein delay, set the maximum refund. For Simple delay, set the protected delay before main time falls.
Enter short player names and confirm First side to move. The summary badge should name that side as ready to move first.
Open Advanced if you need a different Low-time warning or audible Boundary tones. Set the tone volume before starting if sound is enabled.
Press Start. After each move, press the active clock face or Switch turn. If the setup shows Starting time must be above 0 seconds., raise the starting time before trying again.
Use Pause for an interruption and Reset game only when the current session should be cleared. Reset adds a fresh setup event and returns both clocks to the selected starting time.
Review Current Clocks, Time Control Brief, Move Ledger, Clock Balance Trace, or JSON when you need to copy, download, or inspect the session state.

Interpreting Results:

Start with the summary strip. Ready, Live, Paused, and Flag tell you whether the game is waiting, running, interrupted, or over on time. The active-side badge names whose clock is expected to run next.

How to read chess clock timer result cues
Result cue	What it means	What to verify
`Clock margin clear`	Neither clock is at or below the low-time threshold.	Confirm the threshold still fits the selected time control.
`White low time`, `Black low time`, or `Both under pressure`	At least one side is at or below `Low-time warning`.	Check whether the warning was intentionally set or left at the default 30 seconds.
`Flag`	A clock reached 0 and the session stopped.	Read the final ledger row and the visible clock before deciding what the game result should be.
`Spent`	Time below the original starting time, not total thinking time.	In Fischer games, a player can think and still show little or no spent time because increment restored the clock.

A clean-looking chart or ledger does not prove the chess position, legal-move status, or tournament result. Use those outputs to review clock handling and session history, then apply the game rules agreed before play began.

Worked Examples:

Blitz 5+3 with Fischer increment

Choose Blitz 5+3 and leave First side to move on White. If White spends about 2.4 seconds and presses Switch turn, White's clock drops and then receives the 3-second increment. The display can round up to about 5:01, Move count becomes 1 ply, and Current Clocks shows White with one move completed.

Simple delay for a slow practice game

Set Custom, Simple delay, Starting time to 10 min 0 s, and Delay to 5s. When Black is on move and uses only three seconds, the main black clock still reads 10:00 after the switch because the protected delay absorbed that thinking time. If Black thinks for eight seconds, only the three seconds beyond the delay are charged.

Bronstein delay near the threshold

Set Bronstein delay with 15 min 0 s starting time and a 10s delay refund. A seven-second move is fully refunded and returns to 15:00. An eighteen-second move refunds only ten seconds, leaving about 14:52. That boundary is why Bronstein delay can feel forgiving without letting a player bank unused bonus time.

Setup mistake before a game starts

If Starting time is set to 0 min 0 s, the page shows Starting time must be above 0 seconds. and the clock cannot start. Raise either minutes or seconds, confirm that the summary returns to Chess clock ready, and then use Start again.

FAQ:

What is the difference between Fischer and Bronstein timing?

Fischer timing adds the selected increment after every completed move. Bronstein timing refunds only the time used up to the selected delay and never raises the clock above the value shown at the start of that move.

Why did the active clock not lose time in simple delay mode?

In Simple delay, the main clock waits until the delay expires. If the player presses before the delay runs out, the main time stays unchanged for that move.

Can the clock be used for a rated tournament game?

Use it for practice, casual games, and review. Formal events should follow the organizer's equipment rules, clock-placement rules, claim procedures, and arbiter instructions.

Why is the balance chart empty or short?

The chart is built from recorded events. Start the clock, switch turns, pause, reset, or reach a flag to add more points to Clock Balance Trace.

Does the session state need a server calculation?

No. The clock state, ledger, chart data, table exports, and JSON summary are handled in the browser after the page loads. Copied and downloaded files are still your responsibility to store or discard.

Glossary:

Chess clock: Two connected time displays where only the player to move spends time.
Flag: The state reached when a player's allotted time expires.
Fischer increment: Bonus time added after a completed move, which can increase the remaining clock.
Bronstein delay: A refund of spent time up to the delay amount, capped at the pre-move clock value.
Simple delay: A protected period at the start of each move before main time begins falling.
Ply: One move by one player, so a White move and a Black move count as two ply.
Low-time warning: The selected threshold where the summary and clock rows mark a side as under pressure.

References:

FIDE Laws of Chess taking effect from 1 January 2023, International Chess Federation, 2023.
Rule Book Updates and Changes, US Chess.
Time Controls, Chess.com.