Why does my guitar go out of tune so fast?

Rapid tuning instability has a handful of usual-suspect causes, and the fix is almost always cheaper and simpler than people expect — this is rarely a "something is fundamentally wrong" situation.

New strings that haven't stretched in

Brand new strings will go flat repeatedly during their first hours of use as they stretch and settle in. This is completely normal and not a defect. Stretching them manually (gently pulling each string away from the fretboard a few times, then retuning, repeated a few times) speeds up the process significantly.

Binding at the nut

If a string doesn't slide smoothly through its nut slot, tension can build unevenly and release suddenly when you bend a note or even just play normally, causing the string to slip out of tune. A slot that's too narrow, rough-cut, or has a burr will cause this. Graphite or a proper nut lubricant, or a proper reslotting if the issue persists, addresses it.

Tuning peg issues

Worn, loose, or slipping tuners can't hold tension reliably, and this shows up as a slow, steady drift out of tune rather than a sudden jump — a useful distinguishing clue versus nut binding, which tends to cause more sudden slips.

Improper string winding at the post

Too few winds, too many winds, or winds stacked messily on top of each other on the tuning post can all cause instability, since the string isn't seated as securely or consistently as it should be.

Bridge or saddle issues

On guitars with moving bridge parts (tremolo systems especially), an unbalanced spring tension or a bridge that's not sitting level can cause tuning to shift with normal playing, particularly with bends or vibrato.

The practical approach

Rule out new strings first (give it a day or two of playing). If it's still unstable after that, check nut slots, tuner condition, and winding technique in that order — they're the most common causes, roughly in order of likelihood.