A double check happens when a single move puts the enemy king in check from two pieces at once: the piece that just moved gives check itself, and its move also unmasks a check from another piece that was hiding behind it. It’s the most violent form of a discovered attack.

Why the king always has to move

Against a simple check, there are three possible answers: move the king, block the attacking line, or capture the checking piece. Against a double check, two different attacking lines threaten the king at the same time: blocking or capturing just one piece always leaves the other check active. That leaves only one legal option: move the king.

The knight jumps to c7: it checks the king directly while also unmasking the rook's check on the e-file. Double check: the king must move.

In this position, the knight jumps from e6 to c7. It attacks the black king directly from its new square, and by leaving e6 it clears the e-file for the white rook, which also attacks the king. Both checks are active at the same time: there’s no way to parry both except by moving the king.

A fearsome weapon in practice

Double checks are rare, but often decisive: since the king has no choice but to move, the opponent can neither defend the king any other way nor counterattack. It shows up frequently in mating combinations, most famously the “smothered mate,” where a knight uses a double check to force the king onto a fatal square.

Frequently asked questions

Can a double check be answered by capturing one of the two pieces?

No. Even if one of the two checking pieces can be captured, the other keeps attacking the king after the capture: the king would still be in check, so that move would be illegal. Only moving the king itself remains possible.

What’s the difference between a double check and an ordinary discovered attack?

In a regular discovered attack, only the unmasked piece gives check; the piece that moves doesn’t give check itself — it may well threaten something else. In a double check, both pieces (the one that moves and the one that’s unmasked) give check at the same time.

Can a double check deliver checkmate?

Yes, very often. Since the king is forced to move, if it has no safe square to go to, the double check immediately becomes checkmate. It’s one of the most common ways to deliver mate in practice.