How the speed actually changes
Every GIF frame carries its own delay. Speeding up means shortening those delays, not discarding frames, so nothing is lost and the file size does not change. Slowing down lengthens them, which is why a slowed GIF is no larger than the original.
That is different from how video is usually retimed, and it is why a GIF can be sped up and slowed back down with no loss at all.
The floor nobody mentions
Browsers refuse to honour delays below about 20 milliseconds — a legacy rule from an era of slow machines — and quietly substitute 100ms instead. A GIF asked to run at 100fps therefore plays at 10fps, far slower than intended.
So there is a practical ceiling around 50fps. Past that, drop frames rather than shortening delays: the compressor can remove every second frame, which speeds up playback and shrinks the file at the same time.
Frequently asked questions
Does speeding it up lose frames?
No — only the delays change. Every frame is still there, which is why the file size stays the same and why the change is completely reversible.
Why will it not go any faster?
Browsers ignore frame delays under roughly 20ms and use 100ms instead, so asking for extreme speed makes it slower. Around 50fps is the practical ceiling; beyond that, remove frames instead.
Will slowing it down make the file bigger?
No. The same frames are held longer, so the file is unchanged — only the playback duration grows.
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