The rules, from Meta's Help Center
Threads calls them topics, not hashtags. When you write a post you can tag a topic either with the Tag button or by typing #, and the tagged topic appears in blue. Tapping it shows search results for posts about that topic.
- One topic per post.
- Up to 50 characters.
- Spaces and other special characters are allowed, so "home espresso" works as a single topic.
- The # symbol is optional. Meta notes it may matter for sharing to other fediverse platforms.
- Some topics cannot be tagged at all; Meta's Help Center links to a list of reasons.
Do topic tags help?
Meta says they do. In 2025 it stated that its analysis shows posts that include a topic generally receive more views than those that don't, and its creator guidance recommends adding relevant topic tags to reach people interested in that subject. Meta has not published figures, and "generally receive more views" is not the same as "tagging causes more views": accounts that tag carefully may also be the ones that post carefully.
The practical conclusion is simple. Tagging a relevant topic costs nothing and Meta says it helps on average, so do it on posts that clearly belong to a topic. Do not expect a tag to rescue a weak post.
How to choose the one topic
Because you get only one, the choice matters more than on Instagram, where people spread risk across thirty tags. Three questions help.
Is it what the post is actually about? A post about pricing a freelance design project belongs under freelancing or design pricing, not under a broad trending tag that happens to be popular today. People who tap a topic and find an unrelated post do not engage with it.
Is it specific enough to have a real audience but not so specific that nobody browses it? "Marketing" is crowded; "email marketing" or "newsletter growth" is narrower and closer to what people search for. A topic you invented yourself will usually reach no one unless you are building a recurring series around it.
Is there an active community around it? Since October 2025 Threads has Communities built around popular topics. If your subject has one, its topic is where interested readers already are.
Pro tip
Write the post first, then pick the topic. If you struggle to choose one, the post is probably trying to cover two subjects and would work better as two posts.
Topics and search
Tags are not the only way to be found. Threads has keyword search, so the words in your post matter too. Write the way your reader would search: "how I price logo projects as a freelancer" is both readable and findable. The topic tag then reinforces what the text already says.
Meta has also tested letting people list up to ten topics on their profile, so visitors can see what an account is about at a glance. If that option is available to you, use the same topics you tag most often.
Sources
Platform facts in this guide link to Meta's own documentation, its newsroom or established tech press. Advice without a source is our editorial judgement, not a Meta rule.
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Write content that spreads without hashtags
Frequently Asked Questions
Can I add several hashtags to one Threads post?+
No. Meta's Help Center says you can include up to one topic per post. Plan your post around that one tag instead of a block of hashtags.
Should I include the # symbol?+
It is optional. The topic works the same in Threads either way; Meta says the # may enable extra functionality on other fediverse platforms.
Can I see how a topic performs in Insights?+
Meta has not documented a breakdown by topic tag in Insights. If you want to test tags on your account, compare views on comparable tagged and untagged posts over a few weeks.