Does converting HEIC to JPG lose quality or EXIF data?

Converting to JPG loses a small, usually invisible amount of image quality, because JPG is a lossy format and the photo is compressed again on the way out. Converting to PNG loses none, because PNG is lossless. Either way, the details most people actually care about -- the date a photo was taken, the camera it came from, and its location -- carry over into the result. Here is exactly what changes and what does not.

Why JPG loses anything at all

HEIC and JPG are both lossy: they throw away some detail to make the file smaller, and that trade cannot be undone. Converting HEIC to JPG means decoding the original and re-compressing it as JPG, which is a second round of the same kind of loss. At a high quality setting that loss is not visible at normal viewing sizes or in print -- it shows up, if at all, as very slightly softer detail in fine textures under close inspection, not as an obvious difference.

PNG sidesteps this entirely. It is lossless, so a HEIC converted to PNG has exactly the pixels the decoder produced, with nothing thrown away on the way out. The cost is file size: a PNG is typically five to ten times larger than the same photo saved as JPG.

What the quality slider actually changes

A "Best" or "Smaller file" choice on a JPG conversion controls how much that second compression pass throws away. Best keeps the loss small enough that it is not visible in normal use. Smaller file compresses harder for a meaningfully smaller download, at the cost of visible softening if you look closely or print large. Neither setting exists for PNG, because there is nothing to trade off.

What metadata survives

Most of what people mean by "photo information" does: the date and time the photo was taken, the camera make and model, exposure settings like aperture and shutter speed, and the GPS location if your camera recorded one. That is enough for a photo library to stay sorted and searchable after conversion, which is usually the actual concern behind the question.

What does not carry over: colour profiles (ICC), XMP data, and Apple-specific maker notes. Browsers cannot write those into a JPG or PNG, so a converter that claims to keep everything is overstating it. The gap in practice is small -- these fields matter to photo-editing software more than to the person just trying to open a photo that Windows currently refuses to show them.

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Orientation is a separate, common failure

A photo coming out sideways is not a quality or metadata issue, it is a bug -- usually a converter applying rotation twice, once during decoding and once again from the file's orientation flag. It is worth checking a few converted photos in each rotation (portrait, landscape, upside down) the first time you use any converter, since this is the single most common complaint about HEIC converters generally.

The short version

Expect a small, invisible quality cost converting to JPG and none converting to PNG. Expect your dates, camera details and location to survive either way, and expect colour profiles and Apple-specific fields not to. That is the honest scope of what any browser-based converter can actually do.