Guide
HEIC vs JPG
One is newer and much more efficient. The other opens everywhere. That is the whole trade, and which one you want depends entirely on where the photo is going.
What they are
JPG has been the default photograph format since the early 1990s. Every camera, phone, browser, printer and upload form on earth reads it. It is lossy, it has no transparency, and it stores 8 bits per colour channel.
HEIC is what the iPhone has saved since iOS 11. It uses much newer compression, and it can carry things JPG cannot: transparency, higher colour depth, and several images in one file — which is how Live Photos work. More on the format itself.
File size, which is the real reason it exists
A HEIC is usually around half the size of the same photo as a JPG. Across a library of thousands of photos that is a lot of storage, and it is the entire reason Apple switched.
"Around half" is doing real work in that sentence. The ratio moves a long way with the content of the picture — a detailed landscape and a flat studio shot do not compress alike — so treat it as the shape of the difference rather than a number to plan around. The honest way to find out is to convert one of your own photos and compare.
Compatibility, which is the reason people convert
This is where the two are not close. JPG opens anywhere without a thought. HEIC opens reliably inside Apple's own software and unreliably outside it: Windows needs an extension, older software often refuses it outright, and plenty of upload forms reject the file without explaining why.
Nothing about HEIC's quality or efficiency helps when the file will not open. That is why the practical answer is usually not "which is better" but "which one is this photo going to have to survive".
Quality
At the sizes phones actually save, HEIC holds detail at least as well as JPG while taking less space — that is what the newer compression buys. Converting HEIC to JPG is a lossy step, so it is not free, but at normal quality settings the difference is not something you will see on a photograph.
Converting the other way round would be pointless: it cannot recover anything the JPG already discarded. If you want a lossless copy for editing, PNG is the format to convert to, not JPG.
So which should you keep?
- Keep HEIC for photos that live on your phone and in your own backups. That is where the storage saving is worth something and the compatibility problem never comes up.
- Convert to JPG for anything that leaves — sending to someone, uploading to a form, printing, or archiving somewhere you want readable in twenty years.
- Set the camera to Most Compatible only if you send photos constantly and would rather never think about this again.
Most people want both, which is what converting is for: keep the efficient original, and make a JPG of the one you are about to send.