How Many Times Can You Compress a JPEG Before It Looks Bad?
Every JPEG re-save loses a little quality — but the effect is smaller than most people assume, and there's a specific way to avoid it stacking up.
A JPEG loses a small amount of quality every time it's re-compressed, but in practice a single well-configured compression pass — even a fairly aggressive one — rarely looks bad, because most of the damage from JPEG "generation loss" comes from repeatedly re-saving an already-compressed file multiple times, not from compressing it once, correctly, to a target size.
Why "generation loss" gets worse than people expect
JPEG is a lossy format: every time you save one, it throws away some visual detail to save space. Compress a fresh photo once, and the loss is usually invisible. But if that same file gets re-opened and re-saved again and again — resized in one app, cropped in another, re-uploaded and re-downloaded through a chat app that recompresses it — those losses stack, and by the third or fourth generation, blocky artifacts and smudged detail start showing up even at "high quality" settings.
The one-pass rule
The fix isn't avoiding compression — it's compressing once, from the original, to your actual target, instead of repeatedly nudging an already-compressed file down further. If you need a photo under 100KB, go from your original camera photo straight to 100KB in one pass:
rather than compressing to 300KB first, then compressing that result down again to 100KB — each pass adds its own generation loss on top of the last.
Where this actually bites people
The classic case: a photo gets sent through WhatsApp (which recompresses it), saved from there, then uploaded to a form (which may compress it again). By the time it reaches its destination, it's gone through multiple lossy passes you didn't control individually, and quality suffers more than any single compression step would explain. Starting from the original file, not a forwarded copy, avoids most of this.
If you must re-compress an already-compressed file
It happens — sometimes the original is gone. In that case, compress to the highest quality that still meets your size target rather than the lowest, since you're already starting from a lossy file and don't want to compound it further than necessary.
Everything runs in your browser — nothing is uploaded anywhere during compression.