[ELI5]Why do loading progress bars seem to always stop at 99%
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Usually, at 99%, all the parts have been downloaded and the file needs to be reconstructed back into a whole/usable file.
However, sometime progress bars are purely eye candy. It’s just programmed in to give you the illusion of progress.
% It’s a psychological trick to make you think the task is almost done. If it stopped at 90%, you might think it’s taking too long and give up.
There are two answers here. One is that some types of progress are easier to track than others. So, downloads or pulling files into memory, etc., we can track. Once that’s done, and the progress is “almost complete,” we then have to organize that information to be used, which can take a while, but isn’t easy to track, so we just consider it “one step” and leave the progress bar at “almost finished.”
The other answer is that all progress is a little difficult to track. So, often, you’ll get a product design person saying “how long does it usually take? 1-2 minutes? Great. Every 30 seconds, halve the remaining progress. So, go to 50% at 30 seconds, 75% at 60 seconds, etc. That way people will still feel okay waiting, even though we don’t have any actual information.” Which is fine, usually. The actual purpose of the loading bar is to convince the user not to panic and force-quit/restart the task. But then if you ever run into an actual problem/delay, and you’ve already halved the remaining time six times, you’re just sitting at 99%, and it looks like progress suddenly stopped, even though it’s been fake the whole time.
I guess you mean why does it stop more at 99 than 98 or any other particular number.
Because of how the progression is calculated. If big files are loaded first, there is nothing left but small files. There’s about 1% left, or less, but it doesn’t mean that your computer will handle multiple little files faster than 1 big file, hence the stop at 99%.
Also, this id pure speculation, I don’t know what I’m talking about.
I’ve worked at companies where I’ve made progress bars and I’ll give you the dirty little secret, most progress bars don’t measure anything. They are just there to give the user some type of indication that the application is doing something behind the scenes and not just hanging.
Honestly, it’s typically impossible to measure actual progress. With the variety of CPU speeds, memory, network speeds, etc, it’s impossible for a programmer to know which piece will take what time on different computers someone is running on. So like others have said, some are just timers and they increment after X period of time has passed. Some break it up into steps and based on how many steps are done, increment by a certain percentage. It’s all kind of a mixed bag.
To OP’s actual question, pausing at 99% just means that it is taking longer than the programmer thought it would when they made the progress bar, but it isn’t done yet, so it is letting you know it’s not done while it does everything else it needs to do.
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