How long does a file last?

I like to use a hand file to sharpen my saws but am now thinking I'm using the files past their usefulness. How long do you use a hand file before you chuck it and start new? Lets say on a 20" bar w/ rs chain.

I asked this of my local Stihl dealer yesterday, he said one chain or until you don't see metal filings on the clean surface you are filing on, made sense to me

When it takes too much effort to get an edge on the cutter I change the file. If after two or three strokes on a cutter I don't see or feel a good sharp edge I change the file. I usually touch up the chain after each day or two tanks of gas, which ever comes first. (Unless I find buried treasure .)

Not long, or your skill level improves or your pocket is too light!

When I start with a new file, I can feel the teeth biting into the chain as I file. After a while (it varies), I can tell that there is very little resistance when I'm pushing the file, i.e., the teeth are no longer sharp enough to bite into the metal. I also try to rotate the file after each stroke and to push the file down its entire length, to get maximum utilization from each file (i.e., I'm cheap).

Rotate the file as you push and clean the file lightly with a soft wire brush when you're done also. I don't think there is any rule of thumb for file life. You can tell when the file is dull just by the way it pushes.

Helps it last longer to not pull it backwards thru the cutter,
Clean often with brake clean/ gasoline/ degreaser - to keep the oil off so it don't plug up.

Old timers used to clean/degrease them & leave them overnight in battery acid ,
would sharpen them up as it eats away the metal evenly. rusty but sharper.

I just bought a dozen Oregon, on sale, should be good for 12 years @ 1 per year
Cheaper by the dozen

I get 2 rs chains per file, then go new.