In short: A serious mistake that gives away material or the game, usually because you have overlooked something. In annotations it is marked with two question marks, ??.
A blunder is a serious mistake: a move that gives away a piece, lets your opponent mate or ruins a good position. Usually it isn't because you don't know better, but because you have overlooked something. Time trouble, overconfidence and carelessness are the most common causes.
A classic blunder
Black wants to drive the queen away from h5, but forgets to look at what it threatens.
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The mate has a name of its own, scholar's mate, and it is easy to stop. All it takes is seeing the threat.
Question marks and exclamation marks
In annotations and chess books, moves are marked with signs after the move.
| Sign | Meaning |
|---|---|
| ! | a good move, often a surprising one |
| !! | an excellent move, often a decisive one |
| ? | a bad move, a mistake |
| ?? | a blunder, a move that gives the game away |
| !? | an interesting move, which need not be the best |
| ?! | a dubious move, which may turn out to be bad |
| □ | the only move, the one that has to be played |
| TN | a theoretical novelty, a move not played before |
Where the line falls between a mistake and a blunder is a judgment call. The same move can be an ordinary mistake by a beginner and a blunder by a grandmaster. Signs like += and +− are about the position instead; see advantage.
How to avoid blunders
- Ask what your opponent threatens. Do it after every move your opponent makes. It is the most important habit of all.
- Check your own move. Before you let go of the piece: is it safe, and does the move leave anything else hanging?
- Save time. Many blunders are made in time trouble.
Many players used to write the move on the scoresheet before playing it, to get one last chance to think. Grandmasters did it too. Today it is forbidden. If you have played a game here, let the game review show you where the mistakes came.
Frequently asked questions
What do !? and ?! mean?
!? is an interesting move that need not be the best, often a bold try. ?! is a dubious move that may turn out to be bad.
What is the difference between a mistake and a blunder?
It is a judgment call. A blunder is worse: it usually gives away a piece or the game. The same move can be an ordinary mistake by a beginner and a blunder by a grandmaster.
May you write the move down first to avoid blunders?
No. Many players used to do it, grandmasters too, but today it is forbidden to write a move down before you have made it.
Updated November 14, 2026
The starting position. Press ▶ or use the arrow keys.