String Replacement Interval?

[Rabb]

I was wondering what the rule of thumb is for replacing strings.
In other words how do you know it's time to replace them?

[Brent Norton]

Luckily, the rule of thumb is beautifully simple:

When the strings are no longer giving you what you're after (whether it's in the tone, volume, tension, [etc.] or any combination thereof) it's time to change 'em.

[Bassmickeyd]

The oils in your skin are string killers. So, if your a heavy sweater you're going to go through strings. But, if your not and you wipe your strings down after you play, don't eat with your hands when playing a wedding, and wash after useing the bathroom your strings are good for years and years. Me, I'm lucky, I can get about four years out my strings, by looking after them, and washing before going to the bathroom...... think about it.