Canadian byo-yomi: overtime by the stone

How a block works

Canadian overtime has one repeating cycle. Say the setting is 25 stones in 10 minutes:

1. Main time expires. You enter overtime with 10 minutes on the clock and a counter showing 25 stones to play.
2. Each move you make decrements the stone counter. The clock keeps running down through all of them — it does not reset per move.
3. If you play the 25th stone with time still on the clock, the block refills: back to 10 minutes and 25 stones, and the cycle repeats. Any unused time is discarded, not carried over.
4. If the clock reaches zero while you still owe stones, you lose on time.

The practical effect is a budget you spend as you like. Twenty-four seconds per stone is the average, but nothing stops you spending three minutes on a critical fight and then playing ten quick, forced moves to catch up. Japanese byo-yomi never allows that trade.

Why it exists: analog clocks

Canadian overtime was designed to be workable on equipment that could not do byo-yomi at all. A mechanical chess clock cannot reset a period every move — but it can measure a ten-minute block. So the rule was restructured: instead of the clock tracking a per-move deadline, the players count stones, and the clock just runs.

In practice players set aside the required number of stones from the lid of the bowl, then play from that pile. When the pile is empty, the block is done. It is a genuinely clever piece of rule design, and the reason the system is still standard in North American clubs and on IGS-Pandanet decades after digital clocks arrived.

The stone counter is the hard part

Every other Go time system needs only a clock. Canadian overtime needs a clock and a count of stones per player, which is why so few timer apps implement it correctly — and why a chess clock cannot do it at all.

Byoyomi Timer shows the remaining stones next to the running time, decrements them as each side presses the clock, and refills the block automatically when the quota is met. The counter is tappable, because miscounts happen: someone plays two stones on one press, or a stone is placed while the opponent's clock is running. A referee can correct the count without resetting the game.

Common settings

Fewer stones in the same time is harsher, because a single long think eats a larger share of the block. Twenty-five stones in ten minutes is the setting most players find comfortable, and it is what "Canadian" usually means without further qualification.

Progressive overtime: the growing quota

Progressive overtime is Canadian overtime with one change: the stone quota increases with every completed block. A setting might start at 15 stones per 5 minutes, then require 20, then 25, all in the same 5 minutes. The longer the game runs, the faster you must play.

It is rare in Europe and North America but used at events in East Asia. Mechanically it is a small generalisation of Canadian overtime — an increment on the stone count — so Byoyomi Timer offers it as its own system rather than hiding it behind a setting.

A naming warning

Two pieces of terminology cause real confusion. First, Canadian overtime is sometimes called "Canadian byo-yomi", which invites people to expect per-move periods. They are different systems: one deadline covers many stones here. Second, searching for "canadian overtime" without the word Go leads straight to Canadian employment law about overtime pay. Add "go" or "byo-yomi" to the search.