How often do you replace your fishing line?

I have a few reels that the line (Berkley Nanofil) is several years old.  How often do you guys replace your line?

Cotton wood is easy to get off.Pull mono tight and snap it like rubber band. Works better dry than wet but still works both ways.

As others have said, it depends on the reel and application, and frequency of use.  Am I fishing open water trolling, zebra muscles,  rocks etc.  My spinning reels with mono, more often, some of my reels with braid, less often.  One thing I do though is on my line counters I do not replace all the line.  I'll strip off 300-350 yards and refill that much line.

Thats what I do,I just pick it off,if I did not do that I would be replacing line every three hours.That said when all I used was mono I did have to replace mono almost every week of solid fishing.

Some rods that i run mono/floro/copoly I have to refill 3-5 times a year.  I fish rocks a lot.  If you lose 6-8 jigs every time out you're refilling in couple weeks.  I run backing on every mono/floro/copoly.  Old line casts like crap anyway...and once a line gets a lot of twist,  no matter how much you get twist out it seems to come back faster.  It's gone,  respool. 

When the cottonwood flies in June,  I respool almost daily for a week.  you can't cast a rod with that crap in a spool,  a couple pieces and you're done.

Ive fished w people many times and they have a half spool of line. they can't cast for crap and they wonder why.  I don't care if it's brand new a week ago,  if it's too low on that lip, you change it unless you are just vert jigging and don't need a full spool.

PowerPro/braid/nano - when the spool gets too low and I can't get max distance on a cast.  usually every other year.

Mono and copoly is cheap,  if it's 1/8 below the lip it's too low.  If it seems to be holding a ton of memory, lot's of twist, change it.  It's just my feeling on line,  cheapest part of your equipment and one of the most essential.

What BM12 said

Braid - On my primary musky rod it depends on how many fish I have caught and reties of leaders I've done (loss of line capacity on the spool). Usually every season, but have gone 2.  On non-primary musky rods, 2-4 years. 

Mono - on all of my spinning rods for bass, catfish, etc, I change line every year.  Sometimes I have re-spooled 2x during a year.  I have one musky combo that I run 40 lb Maxima mono for special circumstances.  That is changed out every 2 years.

I'm pretty much with Bugle.  Mono or Fluoro is changed every other year or so depending on use.  Braid or other superlines I normally change them out more so because my reels are getting low or the color is fading rather than actual line deterioration. I have new spools of line in storage that I have no problem using or storing for years.

100% depends on how much it gets used.  Any braid or super line lasts at least 4-5 seasons on my reels.  Mono gets changed probably every 2 years and more frequently if it's one of my frequently used combos.  I also tend to refresh spools on my lighter crappie combos that I use in spring.  I use 4 lb test on those and like lighter line fresh.

I maybe use my musky rods a couple of times a year.  I've had the same Power Pro on those for nearly a decade.

Another great trick that I use with super lines for when they get old and start to look frayed is to spool the line onto an old spool and then reel it onto another reel.  Then cut off a few yards of the end of the line that's been used, retie that your original reel and fill the reel.  You now have unused, practically brand new line.