Guitar Strings wear out due to vibration, stretching, corrosion, rust, dust, dirt, oils and sweat. So it’s important to replace them regularly to keem them sounding and feeling great.

As a general rule of thumb you would want to put new strings on electric and acoustic guitars every 24 - 48 playing hours to keep that bright, clean sound and to avoid broken strings. As an example, if you play every day for an hour a day, you should replace your strings every month.
Electric Strings: Replace these at least every 2 months.
Acoustic Strings: Replace these at least every 2 months.
Classical Strings: Replace these at least every 4 months.
Bass Strings: Replace these at least once a year.

Coated strings last upto 5 times longer as they have an anti corrosion coating to protect against the causes of dead strings, so can last up to 6 months or even longer.