Three systems, one comparison
Scroll sideways on small screens to compare all three modes.
| Behavior | Fischer | Bronstein | US Delay |
|---|---|---|---|
| During the move | Main clock counts down | Refund-style clock counts down | Delay runs first; main time then counts down |
| After a turn-ending clock press | Full increment added | Time spent returned, capped at delay | No end-of-move bonus needed |
| Can quick moves grow main time? | Yes | No | No |
| Unused allowance | Full increment is banked | Unused delay discarded | Unused delay discarded |
| 1:00, three-second move | 1:02 after +5 | 1:00 after refund | 1:00 main time |
| 1:00, eight-second move | 0:57 after +5 | 0:57 after refund | 0:57 main time |
The examples use one minute of main time and five extra seconds per move. They show the clock after a completed turn, with enough time left to avoid flag fall. A matching result after an eight-second move does not make all three systems interchangeable.
Fischer: add a fixed amount after the move
With Fischer increment, the main clock runs during your turn. After the player completes a turn and presses the clock, the whole selected increment is added. Moving faster than the increment increases your remaining time; taking longer spends time overall.
Start with 1:00, use three seconds, and earn a five-second increment: the settled clock is 1:02. Use eight seconds instead: it becomes 0:57. The award is five seconds in both cases. Earned time remains available on later moves.
In Chess Clock, the increment is awarded at the turn switch. Both players start at the selected base time, without a separate first-move increment. A clock that has already flagged cannot be revived by a late increment.
Bronstein: return only what was used
With refund-style Bronstein delay, the display counts down immediately. After the player presses the clock before flag fall, the clock returns the smaller of the delay setting and the time actually spent. Your settled main time never rises above the start-of-turn amount.
With 1:00 and a five-second delay, a three-second move takes the display to 0:57 and the press returns it to 1:00. An eight-second move takes it to 0:52 and a five-second refund leaves 0:57. The unused two seconds on the short move are discarded.
Dedicated clocks can present Bronstein allowance in different ways, including combined displays. This page describes the refund calculation and the clock behavior in Chess Clock.
US Delay: wait before spending main time
With US Delay, the first five seconds of the turn are an allowance during which the main clock remains still. A three-second move leaves 1:00. An eight-second move uses three seconds of main time and leaves 0:57.
There is no refund to wait for after the press. The time was protected before it could be spent. Each new turn gets a new allowance, but unused delay disappears at the turn switch. Fast moves do not grow the main-time budget.
Are Bronstein and US Delay equivalent?
They have the same settled main-time cost for a completed move with enough time remaining: the amount by which the thinking time exceeds the delay. Their running displays differ. This is why a player can see a countdown under Bronstein while US Delay still shows unchanged main time.
Do not assume every implementation handles expiration identically. Chess Clock’s Bronstein display counts down the main time and checks for zero before applying the refund. US Delay consumes its allowance first. Near flag fall, a player cannot rely on a future Bronstein refund to recover from an already expired countdown.
For example, if the app’s Bronstein turn begins with two seconds and the delay is five seconds, the player must still press before its displayed countdown reaches zero. US Delay with two seconds of main time protects the initial five-second interval. This is an implementation distinction, not permission to ignore flag fall.
Which system should we choose?
Choose Fischer if you want quick moves to create time for later decisions. Choose delay if you want a fresh allowance on each turn without accumulating unused seconds. Between the delay modes, consider how you prefer to read the clock and understand the app’s expiration behavior.
Agree on the mode and value with your opponent before starting. In an organized event, use the specified format and check device requirements. The app’s tournament positioning is not a claim of certification or universal permission to use a phone.
All three modes are free in Chess Clock
The free app includes Fischer, Bronstein and US Delay, common increment and delay values, 1, 3, 5 and 10 minute time controls, and quick tournament presets. Choose your time, mode and value in setup, review the summary, then Start.
Pro is an optional one-time unlock for custom game lengths, custom increment and delay values and advanced setup. There are no ads and no subscription. Pause/resume and game history are free. For the complete board-side workflow, see the iPhone chess clock guide.
References and scope
The standard distinction between cumulative increment and the two delay displays is described in the US Chess Rules of Chess, 2026, section 5B1c. App availability and the free/Pro boundaries come from the current App Store listing. The worked examples explain clock arithmetic; they are not official time-control classifications.
Product features: Chess Clock on the App Store. Standard timing modes are free; Pro unlocks custom values.