Diagnose
What's going on with your guitar?
Pick the symptom that sounds most like yours. We'll list the likely causes, most common first, and say which ones are safe to fix at home.
Likely causes for
Chords sound out of tune higher up
Intonation not set DIY
The saddles aren't at the right distance, so fretted notes drift sharp or flat higher up.
Old strings DIY
Worn strings lose their even mass and won't play in tune, however well the guitar is set up.
Action very high DIY
Pressing a high string down stretches it, which pushes notes sharp.
Not sure? Start with the first cause. Each guide checks it before you change anything.