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

Quick adjust: {{ baseSliderReadout }}

{{ timingBonusLabel }}:

Quick adjust: {{ bonusSliderReadout }}

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.

Quick adjust: {{ lowTimeSliderReadout }}

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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Time controls make chess a game of allocation as much as calculation. A player is choosing moves, managing risk, and deciding when a position deserves extra seconds from a clock that belongs only to the side on move. Pressing the clock after the board move completes that turn in ordinary clock handling, so a slow hand or a missed press can spend real time even when the move was found quickly.

The notation beside many casual and tournament games compresses two ideas into a short label. A control written as 5+3 usually means five minutes at the start plus three seconds connected to each completed move, but those three seconds can behave in different ways. They may be banked as increment, protected as delay before main time falls, or refunded after the press up to the amount of time actually used.

Base time: The starting clock loaded for each side, such as one minute for bullet or ten minutes for a rapid practice game.
Increment: Extra time added after a move. A player who moves faster than the increment can build time.
Delay: A protected amount of move time that does not become banked time. Delay can be shown as a wait before the main clock falls or as a Bronstein-style refund after the press.
Flag: The moment a player's allotted time reaches zero. In tournament play, the final result can still depend on the rules, mating material, claims, and arbiter decisions.

Chess clock switching time between White and Black with increment and delay modes — Increment can add bankable time, while delay protects or refunds move time without carrying unused seconds forward.

Short controls magnify every second. In bullet and blitz, a player may choose a less ambitious move because the press, reply, and next decision must all happen cleanly. Increment and delay make rapid and longer games less likely to collapse from one awkward moment, but they still reward players who finish moves clearly and keep enough time for difficult positions.

Category names are not universal. FIDE, US Chess, clubs, schools, and casual groups draw the lines between bullet, blitz, rapid, quick, and standard games in different places. Before play starts, the important details are the starting time for each side, the per-move rule, the side to move first, and the local rule for a flag fall.

A browser clock is useful for lessons, puzzle races, opening drills, casual games, and post-game review. Formal events should use the organizer's approved equipment and follow the announced clock placement, pause, flag-claim, and arbiter procedures.

How to Use This Tool:

Set the time control before the first move, confirm which side starts, and use the clock faces or switch control consistently after each completed move.

Choose a Time control preset such as Bullet 1+0, Blitz 3+2, Rapid 15+10, or Classical 25+10. Choose Custom when the agreed control does not match a preset.
Select the Clock mode. Simple countdown uses no per-move bonus, Fischer increment adds seconds after a move, Bronstein delay refunds used time up to the delay, and Simple delay waits before main time starts falling.
Enter the starting minutes and seconds for each side. The exact fields accept unusual controls, while the quick slider is useful for common ranges from 0:30 through 60:00.
Set the bonus seconds, player names, and First side to move. White normally starts, but Black can be selected for drills, odds games, or nonstandard practice positions.
Open Advanced when you want a low-time warning threshold or optional boundary tones. A low-time warning changes the pressure cue only; it does not change the clock math.
Press Start to begin. After each move, press the active clock face or Switch. Use Pause for agreed interruptions and Reset only when the current session should be cleared.
Use Current Clocks, Time Control Brief, Move Ledger, Clock Balance Trace, and JSON for the live clocks, agreed setup, event log, charted clock balance, and structured session record.

Interpreting Results:

The summary shows the frozen game setup once play starts: base time, mode, bonus, starting side, and the current pressure state. The live clock faces show each side's name, remaining time, move count, and status, so they are the first place to check before a press or pause.

Spent is measured against the original starting time, not total thinking time. In Fischer games a fast player can receive enough increment to return above the starting value, so spent time may show as zero even after several moves.

Chess clock result cues and their meaning
Cue or output	What it means	What to check
Ready	The clock is loaded and waiting for the first start.	Confirm the mode, starting side, names, and bonus before anyone moves.
Live	One side's clock is running or its simple delay is counting down.	Check that the active side matches the player to move.
Paused	The current position is interrupted without charging either player.	Resume only after both players agree which side is on move.
Low time	One or both clocks are at or below the selected warning threshold.	Make sure the threshold was intentional, especially in bullet or very long games.
Flag	A running clock reached zero and the timer stopped.	Use the final clock and ledger row as timing evidence, then apply the game rules being used.
Clock Balance Trace	A chart of event points for setup, start, switches, pauses, resets, and flags.	Do not read it as a continuous sample of every fraction of a second between presses.

The exports are records, not arbiters. They can help review the agreed setup and event sequence, but they do not judge legal moves, checkmate, stalemate, insufficient material, draw claims, or whether an organizer accepts a clock claim.

Technical Details:

A chess clock is a paired countdown system with exclusive running state: White's clock or Black's clock runs, not both. The active player's remaining time is reduced until the move is completed, the game is paused, the session is reset, or the clock reaches zero. The press after the board move matters because increment and Bronstein-style refund rules are applied to the player who just moved.

Increment and delay solve different problems. Fischer increment rewards fast play by adding a fixed amount after each move, so unused seconds can accumulate. Delay protects a fixed amount of time per move without letting the player bank unused protection. A visible simple delay waits before subtracting main time; a Bronstein-style delay may show main time falling during the move and then refund the time used up to the selected delay.

Formula Core:

Let R be remaining time in seconds, e be elapsed time on the current move, b be the selected bonus or delay seconds, and R_start be the active player's clock at the start of the move.

R_{next} = \max (0, R_{previous} - charged seconds)

simple delay charged seconds = \max (0, e - b)

R_{after move} = \max (0, R_{before bonus}) + b

R_{after move} = \min (R_{start}, \max (0, R_{before refund}) + \min (b, e))

A 5-second simple delay charges nothing for a 3-second move and charges 3 seconds for an 8-second move. A 5-second Bronstein delay also produces a 3-second net loss for that 8-second move, but the displayed behavior during the move can feel different because the refund is applied at the press.

Mode Rules:

Chess clock mode rules
Mode	During the move	After the move	Can unused time be banked?
`Simple countdown`	Main time falls immediately.	No bonus is added.	No.
`Fischer increment`	Main time falls while the player thinks.	The selected increment is added to the moved side.	Yes. A move faster than the increment can increase the clock.
`Bronstein delay`	Main time falls while the player thinks.	Spent time is refunded up to the delay and capped at the move-start clock.	No. The refund cannot exceed the starting value for that move.
`Simple delay`	Main time waits until the delay expires.	No separate refund is needed.	No. Unused delay disappears after the move.

Bounds and Display Rules:

Chess clock input bounds and display rules
Setting or output	Rule	Practical effect
Starting time	0 to 600 minutes plus 0 to 59 seconds, with total time above 0 seconds. The quick slider covers `0:30` to `60:00`.	A `0:00` setup cannot start, while long casual controls are still possible through the exact fields.
Bonus or delay	0 to 120 seconds, disabled for simple countdown. The quick slider covers 0 to 60 seconds.	The same numeric setting acts as increment, Bronstein refund cap, or simple delay according to the selected mode.
Low-time warning	0 to 600 seconds, with 0 disabling the warning. The quick slider covers 0 to 180 seconds.	The pressure cue changes at or below the threshold, but no time is added, removed, or frozen.
Displayed clock	Normal display rounds remaining seconds up. A running active clock below 10 seconds shows tenths.	The display stays readable during most of the game and becomes more precise near a flag.
Move ledger	The newest 250 setup, start, switch, pause, reset, and flag events are kept.	Long practice sessions keep a recent audit trail without growing indefinitely.

The balance chart is event-based. It records the clock values at meaningful changes rather than sampling continuously, so a flat section between two points means no recorded event occurred there, not that both clocks were unchanged for every instant.

Accuracy and Privacy Notes:

Browser timers are suitable for practice and casual play, but they are not certified tournament equipment. A sleeping device, throttled background tab, low battery mode, heavy browser load, or accidental navigation can affect timing or visibility.

The timing, move log, and exports are handled in the browser session. Player names and setup details can appear in copied tables, downloaded files, JSON, screenshots, and shared state, so avoid private names when the record may be sent to someone else.

For rated or organized play, agree on the exact clock mode and flag procedure before the game starts. This timer models a single two-player time bank per side; it does not replace multi-period tournament clock programming, approved equipment, or an arbiter's ruling.

Worked Examples:

Blitz 5+3 with Fischer increment

Choose Blitz 5+3, keep Fischer increment, and start with White. If White spends 2.4 seconds and presses the clock, White first loses that time and then receives 3 seconds. The visible clock can rise above the original 5:00 because the unused part of each increment is banked.

Simple delay in a practice game

Choose Custom, set Simple delay, enter 10:00 starting time, and set a 5s delay. A move completed in 3 seconds leaves the main clock unchanged. A move completed in 8 seconds spends only the 3 seconds beyond the delay.

Bronstein delay near the cap

A 10s Bronstein delay refunds spent time up to 10 seconds and never raises the player above the move-start clock. A 7-second move returns to the move-start value. An 18-second move loses about 8 seconds.

Low-time warning for bullet

For a 1+0 bullet game, a 30-second warning may be too broad because half the starting time is marked as pressure. Set a smaller threshold or use 0 to turn the warning off.

FAQ:

Why can a Fischer clock go above the starting time?

Fischer increment adds the selected seconds after each completed move. If a player moves faster than the increment, the clock can grow above the original starting value.

Why did simple delay not reduce the clock?

The main clock waits until the selected delay expires. A move completed before that protected time ends does not spend main time.

Is Bronstein delay the same as simple delay?

They often produce the same net time loss for a completed move, but they are displayed differently. Simple delay waits before charging main time, while Bronstein timing refunds used time at the press and caps the refund at the move-start value.

Can this be used for a rated tournament game?

Use it for practice, casual games, lessons, and review. Rated or organized games should use approved equipment and the organizer's clock rules.

Why is the balance chart short?

The chart uses recorded events. Start, switch, pause, reset, or reach a flag to add more points.

Does a flag automatically decide the game?

Not always. A flag shows that a clock reached zero, but the result can depend on the chess rules being used, mating material, claims, and tournament authority.

Glossary:

Allotted time: The time assigned to a player for the game or for a period of the game.
Flag: The expired-time state reached when a player's clock reaches zero.
Fischer increment: Bonus time added after a completed move, which can increase remaining time.
Bronstein delay: A refund of spent time up to the delay amount, capped at the move-start 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 clock cues mark a player as under pressure.

References:

FIDE Laws of Chess, FIDE Rules Commission.
Chess Clock Time Controls, US Chess Sales.