Determining the key while using a capo on a guitar

A customer recently asked how to determine the key of a song on a guitar while using a capo…

Hi John

The key of the song your playing will be different depending on whether your capo is on or off and depending on what chord you play because using a capo alters the key.

The actual chord that you play on the guitar isn’t the chord you actually hear if you use a capo.

This is because every time you move the capo up a fret, the key changes up a semi-tone.

For example, if you have NO capo on your guitar and you play a song in the key of A (where typically the chords would probably be A, D and E), then the key is A.

But if your capo is on, say, the second fret, then when you play chords with your fingers in the shapes A, D and E, you are really playing in the key of B….