Platforms publish a maximum. Creators read the maximum as a target. That single misreading is responsible for more wasted hashtag effort than anything else.
The numbers
Instagram permits thirty. Use eight to fifteen. Above that, marginal tags dilute the classification signal without adding usable reach.
TikTok counts tags against the caption character limit, so the practical ceiling is around twenty. Use three to six. Captions are read, not scanned, and a tag wall reads as spam.
YouTube allows fifteen in the description, but only the first three render above the video title. Those three carry nearly all the value; the rest are filing.
Facebook technically accepts many. Use two or three. Facebook's culture never absorbed heavy tagging and posts that use it look automated.
X caps you at five in practice and rewards one or two. Multiple studies over the years have found engagement declining past two tags on this platform specifically.
LinkedIn handles up to ten. Use three to five, all in professional vocabulary.
Pinterest accepts twenty. Use around eight, treating them as search terms rather than tags, because Pinterest is a search engine wearing a social network costume.
Threads attaches exactly one topic tag per post. Choose the most specific one available.
Why fewer works better
A recommendation system reading your post is trying to build a confident guess about its subject. Five precise tags produce a sharp guess. Thirty tags spanning six loosely related topics produce a blurry one, and a blurry guess means a worse first audience.
There is also an audience-perception cost that never shows up in analytics. A visible block of thirty tags signals "this account is optimising" to every human who scrolls past it, and that erodes trust in a way no reach metric captures.
The exception
Pinterest genuinely rewards more tags than the others, because its discovery model is search-first and its users type descriptive queries. If you work in a visual, project-based niche — interiors, recipes, crafts, weddings — Pinterest is the one place where a fuller tag set earns its keep.