An internal link points to another page on the same domain; an external link points to a different domain. Internal links help Google find your pages and show which ones matter most. External links send readers to sources, and when other sites link to you, those inbound external links (backlinks) are what bring new authority.
You are writing a post and you keep hesitating over links. Should that statistic link to the original study, or will it "leak" traffic? Should you link to your own older post instead? Most of the confusion comes from treating all links as one thing, when the direction of the link changes what it does.
What is the difference between internal and external links?
The only technical difference is the domain in the href. A link from example.com/blog/post-a to example.com/pricing is internal. A link from the same post to developers.google.com is external, also called an outbound link.
| Internal link | External link (outbound) | Backlink (inbound external) | |
|---|---|---|---|
| Points from | Your page | Your page | Another site |
| Points to | Another page on your domain | A page on another domain | Your page |
| Who controls it | You | You | The other site |
| Main SEO job | Discovery, structure, sharing authority inside your site | Citing sources, helping readers | Bringing new authority and trust to your site |
| Example | Blog post linking to your pricing page | Blog post citing a Google doc | A news site citing your study |
The third column is why people mix them up. A backlink is an external link seen from the other end: the same link is outbound for the site that places it and inbound for the site that receives it.
Subdomains are a grey area. blog.example.com linking to example.com is usually counted as internal by SEO tools, but Google treats subdomains as separate sites in some contexts, so check how your crawler is set up.
What do internal links do for SEO?
Internal links let Google discover your pages and understand which ones you consider important. Google's link guidelines put it simply: "Every page you care about should have a link from at least one other page on your site."
Discovery and crawling
Googlebot finds most new pages by following links. A page with no internal links (an orphan) can still be found through a sitemap, but nothing on your site tells Google it matters.
Context through anchor text
The words you link with describe the target page. Google asks for anchor text that is "descriptive, reasonably concise, and relevant to the page that it's on." Internal links are the one place where you choose every anchor, so use it. What is anchor text explains the types.
Sharing authority
Pages that earn backlinks pass some of that value to the pages they link to. Linking from your most-linked page to a page you want to rank is the cheapest ranking lever you have; what is link juice covers how that flow works.
What do external links do for SEO?
Outbound links mostly help your readers and your credibility; inbound ones are what move rankings.
Outbound links: citing sources
Linking to a primary source lets readers check your claims and shows you've done the work. There is no Google document saying outbound links raise your rankings, so don't add them for that reason. Add them where a reader would want the source. Linking out does not "leak" your own authority in any way worth worrying about; how many outbound links per page goes into the numbers.
Inbound links: earning authority
Links from other sites to yours are among the signals Google uses to judge a page's importance, which is why link building exists at all. You can't place them yourself, so they count for more than anything you do inside your own site. How do backlinks work is the longer explanation.
When should external links be nofollow or sponsored?
Mark an outbound link with a rel value when you don't vouch for it or when it was paid for. Google's guide to qualifying outbound links defines three values:
rel="sponsored"
For links that are "advertisements or paid placements". nofollow is still accepted for these, but sponsored is preferred.
rel="ugc"
For links in user-generated content such as comments and forum posts.
rel="nofollow"
For any other link you don't want to vouch for, "when other values don't apply". Google is clear that this is not for every outbound link: "Use nofollow only when you don't trust the source, and not for every external link on your site."
You can combine values, for example rel="ugc nofollow". Internal links almost never need any of these; nofollowing your own pages only makes them harder to discover. Dofollow vs nofollow links covers the history.
How many of each should a page have?
There is no target ratio. Google says there is no "magical ideal number" of links per page. As a working example, a 1,200-word guide might link to 3 to 5 pages on the same site that cover closely related questions, plus 2 or 3 outbound links to the sources it quotes, on top of the navigation. If a link wouldn't help the reader at that point in the text, leave it out.
Internal links redistribute authority you already have; only inbound external links add more. When you need more of those, outreach, digital PR and link exchange are the usual routes. We make Backlinkster, which handles the exchange route: site owners trade one-for-one links inside real articles.
Frequently asked questions
Are external links good for SEO?
Inbound external links (backlinks) are good for the site that receives them; they are among Google's ranking signals. Outbound links don't raise your own rankings directly, but citing good sources makes a page more useful and more credible to readers.
Is a backlink an internal or external link?
A backlink is an external link seen from the receiving side. When another site links to you, it is an outbound external link on their page and an inbound link, or backlink, to yours.
Do internal links count as backlinks?
Not in the usual sense. SEO tools count backlinks from other domains only. Internal links still pass authority between your own pages, but they don't add any new authority to your site as a whole.
Should I open external links in a new tab?
It's a usability choice, not an SEO one. Google's link guidelines don't mention it. Many sites open outbound links in a new tab so readers don't lose their place; screen-reader users may prefer a warning when that happens.
Should I nofollow all external links?
No. Google says to use nofollow "only when you don't trust the source, and not for every external link on your site." Use rel="sponsored" for paid links and rel="ugc" for user-generated links, and leave ordinary editorial citations followed.
Related: What are internal links in SEO? · How to check internal links on your website · How many outbound links per page? · Dofollow vs nofollow links · How do backlinks work?