Chessy
What Is a Blunder in Chess?
A blunder is a very bad move that seriously worsens your position — typically hanging material or missing a big threat.
What makes a move a blunder
Not every mistake is a blunder. A slightly inaccurate move might lose a small edge, but a blunder is a serious, position-changing error — leaving a piece undefended, walking into a fork, or missing a forced mate. The common thread is a big, avoidable swing in evaluation.
How blunders are marked
In chess notation and on engines, a blunder is flagged with ?? after the move, distinguishing it from a mere mistake (?) or an inaccuracy (?!). Analysis tools like the ones built into Chessy detect these swings automatically and show exactly where the evaluation collapsed.
Why blunders happen
Time pressure, tunnel vision on your own plan, and simply not checking your opponent's threats are the usual causes. Even strong players blunder — it's a normal part of chess, not a sign you can't improve. The fix is a habit: before every move, ask what your opponent's best reply is.
Reducing your blunder rate
The most reliable way to cut down on blunders is deliberate practice — reviewing your own games to see why a move was bad, not just that it was. Pattern recognition for common tactics (forks, pins, back-rank threats) does most of the work of preventing them before they happen.
Frequently asked questions
What is a blunder in chess?
A very bad move that seriously worsens your position, usually by losing material or missing an opponent's threat.
How is a blunder marked in notation?
With two question marks (??) after the move, such as Qxh7??.
Is a blunder the same as a mistake?
No. A mistake (?) is a smaller error; a blunder (??) is a much larger, more damaging one.
Can strong players still blunder?
Yes, blunders happen at every level, including grandmaster games — they're usually caused by time pressure or overlooking a specific threat.