Byo-Yomi: the overtime timer of Go and Shogi
How byo-yomi works, precisely
Byo-yomi (Japanese for "counting seconds") is the traditional overtime system of professional Go and Shogi. It has two stages:
- Main time: a normal countdown you spend freely, like any chess clock.
- Overtime periods: when main time reaches zero, you enter byo-yomi. You have, say, 5 periods of 30 seconds. Each move must now be completed within the current period.
The crucial rule — and the one every newcomer gets wrong — is what happens to a period when you move:
- If you complete your move within the period, the period resets to its full length for your next move. It is not consumed. You could play a thousand moves at 29 seconds each and still have all 5 periods.
- If you exceed the period, it is consumed permanently, and the next period starts counting for the same move. Spend 65 seconds on one move and you burn two full 30-second periods, with the third running.
- Exceed your last period and you lose on time.
In professional Go, an official historically read the seconds aloud — hence the name — but digital clocks now beep or display the countdown instead.
Walkthrough: 30 minutes + 5×30s
Take the byo-yomi preset in Chess Clock: 30 minutes of main time plus five 30-second periods. A realistic game might unfold like this:
- Moves 1–80: you think freely and use up your 30 minutes of main time. The clock hits zero — but you are not out; you enter byo-yomi with 5 periods intact.
- Moves 81–120: you settle into a rhythm, playing each move in 10–25 seconds. Every move resets the 30-second period. You still have all 5 periods.
- Move 121: a genuinely hard position. You spend 50 seconds. The first period is consumed; you complete the move in the second period, which then resets. You now have 4 periods left.
- Endgame: you budget your remaining periods like extra lives — routine moves inside 30 seconds are free, and you can afford at most three more long thinks for the rest of the game.
This is byo-yomi's character: relentless steady pressure, punctuated by a limited allowance of deep thinks. Nothing in chess timing feels quite like it.
Byo-yomi vs. Fischer vs. Bronstein
| System | When time is granted | Can time accumulate? | Character |
|---|---|---|---|
| Byo-yomi | Fixed period per move after main time ends | No — each period resets, never grows | Constant per-move deadline with limited "extra lives" |
| Fischer increment | Seconds added every move, from move one | Yes — fast play banks time | Rewards efficiency; clock can grow |
| Bronstein delay | Thinking time refunded up to a cap, every move | No — clock never grows | Protects against instant-move losses only |
The philosophical difference: Fischer and Bronstein modify how a single pool of time drains, while byo-yomi replaces the pool entirely with a per-move deadline once main time is gone. That guarantees every future move gets the same minimum thinking time — which is exactly what long Go and Shogi endgames need, where a game can run past 200 moves.
There is also Canadian byo-yomi, a Go variant in which a player must play a set number of stones (say, 25) within a shared block of time (say, 10 minutes) — a compromise that is easier to operate on a simple analog clock.
Using a chess clock app as a Go or Shogi timer
Go and Shogi players are chronically underserved by timer hardware: dedicated Go clocks with proper byo-yomi support are niche and expensive, while cheap chess clocks usually offer only delay and increment. A chess clock app that implements true period-based byo-yomi covers the gap.
Chess Clock includes a byo-yomi preset (30 minutes + 5×30s periods, part of Pro) and lets you build custom byo-yomi controls with your own main time, period length, and period count — 10 minutes + 3×20s for a quick Go game, or 60 minutes + 5×60s for a serious Shogi match. The display counts down the active period and shows how many periods remain, the screen stays awake for the whole session, and it works fully offline — no ads interrupting a two-hour game, no account, no tracking. Because each player can be given a different control, you can even give a weaker Go player extra periods as a handicap alongside the traditional stone handicap.
Turn your iPhone into a real chess clock
Chess Clock gives you every time control from Bullet to FIDE Classical — beautiful, precise, and completely private.
Coming soon to the App Store