Footnotes and References in Substack: A Complete Guide

Formatting

Footnotes add a layer of depth to your newsletter without cluttering the main text. They let you cite sources, add context, share tangential thoughts, and demonstrate rigor — all without interrupting the reader’s flow through your primary argument.

Substack has built-in footnote support, making it one of the few newsletter platforms that handles this well. Here’s how to use footnotes effectively.

Substack’s Built-In Footnote Feature

Substack offers a native footnote system that works in both the web version and email delivery.

Adding a Footnote

Place your cursor where you want the footnote marker to appear
Click the footnote icon in the toolbar (or use the keyboard shortcut)
Type your footnote content in the editor that appears
The footnote marker (a superscript number) appears in your text
The footnote content appears at the bottom of the post

How Footnotes Render

On the web: footnote markers are clickable superscript numbers. Clicking a marker scrolls the reader to the footnote at the bottom of the post. Clicking the footnote scrolls back to the marker. This bidirectional linking is smooth and reader-friendly.

In email: footnote markers are superscript numbers linked to the web version of the post. When a reader clicks a footnote marker in their email client, it opens the web version scrolled to that footnote. The footnotes themselves appear at the bottom of the email.

This means email readers can see the footnotes without leaving their email client, but the bidirectional click-to-jump behavior only works on the web.

Footnote Numbering

Substack numbers footnotes sequentially and automatically. If you add a footnote between two existing footnotes, the numbering adjusts. You don’t need to manage numbers manually.

When to Use Footnotes

Source Citations

The most traditional use. When you make a factual claim, a footnote can point to the supporting evidence:

Your text: “Newsletter open rates have declined by 5 percentage points over the past three years.”¹

Footnote: ¹ Source: Mailchimp Email Marketing Benchmarks Report, 2025.

Tangential Context

When a point is interesting but would derail the main argument:

Your text: “Substack’s growth has been remarkable.”²

Footnote: ² Substack crossed 35 million active subscriptions in late 2025, though the company doesn’t disclose the breakdown between free and paid subscribers.

Definitions and Explanations

For readers who might not know a technical term, without patronizing those who do:

Your text: “The company’s CAC has increased significantly.”³

Footnote: ³ Customer Acquisition Cost — the total cost of marketing and sales divided by the number of new customers acquired.

Methodological Notes

For data-driven newsletters, footnotes can explain how you calculated a number or where your data came from:

Your text: “Revenue grew 23% year-over-year.”⁴

Footnote: ⁴ Based on reported Q4 figures, adjusted for currency fluctuations using the average EUR/USD rate for the quarter.

Humor and Personality

Some writers use footnotes for asides, jokes, or personal commentary. This style — popularized by writers like Matt Levine — turns footnotes into a secondary narrative layer that rewards close readers.

Footnotes vs. Inline Links

Both footnotes and inline links accomplish similar goals — providing additional context or sources. Choosing between them depends on the situation.

Use Inline Links When

The source is a specific web page you want readers to visit
The linked content directly extends the current sentence
You want readers to click immediately
The reference is central to your argument, not supplementary

Use Footnotes When

The citation is for credibility, not for the reader to follow
The additional information would break the reading flow
You’re referencing multiple sources for one claim
The note is tangential but valuable
You want to maintain clean, uncluttered prose

The Hybrid Approach

Many effective newsletters use both. Inline links for action-oriented references (“see this tool,” “read this article”) and footnotes for citations and tangential context. This gives readers two levels of depth without cluttering either.

Footnote Best Practices

Keep Footnotes Concise

A footnote should be one to three sentences at most. If your footnote needs multiple paragraphs, it’s no longer a footnote — it’s content that should be in the main body or a separate post.

Don’t Over-Footnote

If every sentence has a footnote marker, the post feels like an academic paper rather than a newsletter. The superscript numbers become visual noise.

Guidelines:

Light use: 2-5 footnotes per post — adds rigor without cluttering
Moderate use: 6-10 footnotes — appropriate for data-heavy or research-based posts
Heavy use: 10+ footnotes — only if your publication’s style is built around it (like Matt Levine’s Money Stuff)

Front-Load Context, Footnote the Details

Put the most important information in the main text. Footnotes are for secondary details:

Good: “Revenue grew 23% year-over-year¹” — the growth rate is in the text; the methodology is in the footnote.

Not ideal: “Revenue changed significantly¹” — the actual number is buried in the footnote.

Be Consistent

Choose a footnote style and stick with it across posts:

Always cite sources in footnotes (not sometimes inline, sometimes footnotes)
Use the same level of detail in citations
If you use footnotes for humor, do it regularly so readers know to check them

Footnotes in Markdown

Standard markdown footnote syntax looks like this:

Here is a claim that needs a source[^1].

[^1]: Source: Research Paper Title, Author, 2025.

However, Substack’s footnote system is proprietary — it doesn’t use standard markdown footnote syntax. If you draft in markdown and convert to Substack-ready rich text using a tool like DownStack, you may need to add footnotes manually in Substack’s editor after pasting.

This is one area where Substack’s editor has an advantage: its native footnote system handles the numbering, linking, and rendering automatically.

Workaround for Markdown Writers

If you want to track footnotes in your markdown draft, use a convention like [NOTE: footnote text] inline. After pasting the converted content into Substack, search for these markers and replace them with Substack’s native footnotes.

Alternative Approaches

Parenthetical References

Instead of footnotes, some writers use parenthetical citations inline:

“Revenue grew 23% (source: company Q4 earnings report).”

This keeps everything in the main text and avoids the need for footnotes entirely. It works well for newsletters with a casual tone.

End Notes Section

Instead of using Substack’s footnote system, you can create a manual “Sources” or “References” section at the bottom of your post with a simple list:

Sources

Email marketing benchmarks: Mailchimp Report, 2025
Subscriber growth data: Substack blog post, October 2025
Revenue figures: Company SEC filing, Q4 2025

This approach is simpler but loses the bidirectional linking that Substack’s native footnotes provide.

Inline Superscript Numbers

If you want footnote-style markers without using Substack’s native feature, you can manually type superscript numbers. However, Substack’s editor doesn’t support superscript formatting, so you’d need to use Unicode superscript characters (¹ ² ³ etc.) — which is more effort than using the built-in feature.

Email Considerations

Footnote Position

In email, footnotes appear at the very bottom of the message — after all your content, CTAs, and the subscription management links. Readers have to scroll all the way down to see them.

This means email readers are less likely to check footnotes than web readers. For essential information, keep it in the main text. Reserve footnotes for truly supplementary content.

Click Behavior

Clicking a footnote marker in email opens the web version of the post. This takes the reader out of their email client, which is a friction point. Some readers won’t bother.

For this reason, don’t put essential information exclusively in footnotes. The main text should always stand on its own.

Key Takeaways

Substack has built-in footnotes with automatic numbering and bidirectional linking on the web
Use footnotes for source citations, tangential context, definitions, and methodological notes
Keep footnotes concise (1-3 sentences) and use them judiciously (2-10 per post)
Choose between inline links and footnotes based on whether you want readers to follow the link or just note the source
Front-load important information in the text; relegate details to footnotes
Email readers are less likely to check footnotes — don’t hide essential information there
Markdown footnote syntax doesn’t map directly to Substack’s system; add footnotes in the editor after pasting
Be consistent with your footnote style across posts to set reader expectations