How social media algorithms work (Instagram and TikTok)
How the Instagram and TikTok algorithms work: official signals (watch time, likes, sends), the first push, organic reach and what you can do.
In 30 seconds
- An algorithm is the system that chooses, for each person, which content to show and in what order, looking for what interests them most.
- For Instagram the three most important signals are watch time, likes and sends (Adam Mosseri, January 2025).
- TikTok uses interactions, video information and device and account settings; follower count is not a direct factor.
- In the EU, the Digital Services Act requires very large platforms to also offer a non-personalised feed.
A social media algorithm is the system that chooses, for each person, which content to show and in what order. There’s no chronological order that’s the same for everyone: the algorithm tries to guess what interests you most by looking at what you’ve done before (what you watch, save, follow) and how other people react to each piece of content.
How algorithms work, in general
Algorithms aren’t public in detail and change often, but the principles are known: Instagram and TikTok, for example, explain them on their official pages. And they’re similar across platforms:
- Interest: what kind of content that person usually watches.
- Reactions to the content: how long people watch it (to the end?), whether they save, share or comment.
- Relationship: whether the person often interacts with that account.
- Content information: text, audio, topic, how recent it is.
How the Instagram algorithm works
Instagram doesn’t have just one algorithm: feed, stories, Explore and reels each have their own system, because people use them differently (stories to see friends and accounts they follow, Explore and reels to discover new things).
The three main signals
In January 2025 Instagram’s head, Adam Mosseri, explained that the three signals that matter most are:
| Signal | What it means | Number to watch |
|---|---|---|
| Watch time | How long people watch | Average reel watch time |
| Likes | How much people like it | Likes ÷ reach |
| Sends | How often it’s sent privately to someone | Sends ÷ reach |
According to Mosseri, likes matter a bit more for reaching people who already follow you, sends a bit more for reaching new people.
Recent changes worth knowing
- Originality: since April 2024 Instagram has said it replaces reposted content in recommendations with the original, to reward creators.
- Trial reels: a feature that shows a reel to non-followers first, so you can see how it does without “bothering” followers.
- Account status: in professional account settings you can see if any content has been excluded from recommendations for breaking guidelines.
How the TikTok algorithm works
TikTok explained how its For You page works in an official post on 18 June 2020. The system uses three groups of signals:
- Interactions: videos you like or share, accounts you follow, comments, content you create, videos watched to the end.
- Video information: captions, sounds, hashtags.
- Device and account settings: language, country, device type. These weigh less, because they aren’t actively chosen preferences.
The strongest signal is whether someone watches a video to the end. And TikTok states that neither follower count nor previous high-performing videos are direct factors: even a new account can reach lots of people if the video works.
The first push and organic reach
New content is first shown to a small group of people (on Instagram mostly followers, on TikTok also strangers with similar interests). If they react well, it’s shown to more people, and so on. That’s why timing matters: if you post while your followers are asleep, the first push is weak.
Organic reach is the number of people reached without paying. On Instagram you’ll find it in Insights, split between followers and non-followers: if non-followers grow, the algorithm is showing your content to new people.
At the fictional shop Five Leaf, posts published at 3 am reached less than half as many people as those at 7 pm, with similar content.
Algorithms and EU rules
Under the Digital Services Act (Regulation (EU) 2022/2065), very large platforms must explain the main parameters of their recommender systems and offer at least one option not based on profiling. Since August 2023 EU TikTok users can switch off personalisation of the For You page, and Meta has introduced similar options for Facebook and Instagram. For creators little changes: most people stay on the personalised feed.
What you can do: 7 practical rules
- Post when your audience is online: you’ll find it in your account analytics.
- Grab attention in the first 2-3 seconds of a video: that’s when people decide whether to keep watching.
- Make content worth saving or sending: guides, recipes, lists, answers to common questions.
- Create original content, don’t repost other people’s.
- Reply to comments: conversations are a positive signal and build relationships.
- Write clear captions: text and subtitles help the algorithm understand the topic.
- Measure and adjust: look at what works on your account, not generic advice. How to read the numbers is explained in social media metrics and in engagement rate: what it is and how to calculate it.
Sources
- Instagram shares algorithm insights for 2025 (Social Media Today, 22 January 2025)
- Instagram is updating its ranking systems for original creators (TechCrunch, 30 April 2024)
- How TikTok recommends videos #ForYou (TikTok Newsroom, 18 June 2020)
- EU users can switch off TikTok personalisation (Il Post, 23 August 2023, Italian)
Which signal tells the algorithm most clearly that content is useful?
Correct! Saving and sharing are strong actions: they say the content is worth coming back to or showing others.
Not quite. Hashtags help little in understanding content, and at night your audience isn't there: the first push is missing.
Frequently asked questions
Is the algorithm the same on every platform?
No, each has its own and it changes often; even within one app there are different systems (on Instagram for feed, stories, Explore and reels). The principles are similar though: the person's interests, reactions to the content, relationship with the poster.
Do hashtags still help?
A little. They help explain what content is about, together with text, audio and images, but they don't get a post to more people on their own. A few relevant hashtags beat thirty generic ones.
What is a shadowban?
It's the name people give to the feeling that an account is being shown less without warning. Platforms talk instead about content «not eligible for recommendations» when it breaks their guidelines: on Instagram you can check this under «Account status».
Does buying followers help?
No. Fake followers don't react to content, so they lower your percentages and the account reaches fewer real people. And it usually breaks platform rules.
Does reposting other people's videos work?
Less and less. Since April 2024 Instagram has said it shows the original in recommendations instead of reposted copies, to reward original creators.
Topics:Social media