How to segment email subscribers by sign-up source in Klaviyo

How to use sign-up source for segmenting email subscribers?

TL;DR: To segment email subscribers by where or how they signed up, use the $source profile property in Klaviyo's segment builder. Navigate to Audience > Lists & Segments > Create Segment, then add the condition Properties about someone > $source > equals > [your source value]. Source values can appear as text labels like "Embedded Form," "Modal," or "Flyout," or as numeric codes like -4 or -3. Use whatever your account displays. Keep in mind that $source can be overwritten by later sign-up actions, so if you need permanent first-touch attribution, store a custom property at the time of opt-in instead.

Why segmenting by sign-up source matters

Knowing where a subscriber came from gives you a meaningful signal about their intent and context. Someone who signed up through a homepage popup may need a different welcome experience than someone who opted in via a checkout embed or a targeted landing page form.

Segmenting by sign-up source lets you:

• Tailor welcome flows and discount offers to match the context of the opt-in
• Measure which forms are driving your highest-quality subscribers
• Personalize messaging based on what you already know about how someone found you

According to eMarketer data cited in Klaviyo's own resources, 39% of email marketers who practice list segmentation see better open rates — and source-based segmentation is one of the most underused ways to get there.

How Klaviyo tracks sign-up source

Klaviyo automatically sets a profile property called $source when a contact is added to your account. This property records the channel or method through which the profile was created — for example, a specific Klaviyo sign-up form, an API call, a manual import, or a third-party integration.

What $source values look like

Depending on your account and how profiles were created, $source may display as:

• Text labels - e.g., "Embedded Form", "Modal", "Flyout", or the name of a specific form
• Numeric codes - e.g., -4, -3, -2 (used for certain integrations or import methods)

When building your segment, use whatever value your account actually displays. You can check this by opening a profile that signed up via the source you want to target and looking at their profile properties.

Important limitation: $source can be overwritten

$source is not a permanent first-touch field. If a subscriber later submits another form or is re-added through a different channel, the $source value on their profile may be updated to reflect the most recent action.

If you need reliable, original sign-up attribution that won't change over time, see the workaround in the section below.

How to build a segment by sign-up source

Option 1: Segment by a Specific Sign-Up Form

Use this when you want to identify everyone who signed up through one particular Klaviyo form (e.g., a homepage popup or a landing page embed).

1. Go to Audience > Lists & Segments
2. Click Create list / segment, then select Create segment
3. Name your segment clearly (e.g., "Signed up – Homepage Popup")

4. Add the condition: Properties about someone > $source > equals > [Your Form Name]

   • The form name here is the name of your Klaviyo sign-up form as it appears in your account
   • To include multiple forms, click Add condition and select OR, then add another $source condition for each additional form
5. Optionally add: If someone can receive email > is > true to filter to active subscribers only
6. Click Save and review the member count

Option 2: Segment by Channel or Source Type

Use this when you want to group subscribers by the type of source (e.g., all embedded forms, all modal popups, or all API-added profiles).

1. Go to Audience > Lists & Segments
2. Click Create list / segment, then select Create segment
3. Name your segment (e.g., "Signed up — Embedded Form")

4. Add the condition: Properties about someone > $source > equals > [e.g., "Embedded Form" or -4]

   • Use the exact label or code shown in your account
5. Layer additional filters as needed (e.g., subscription status, date range)
6. Click Save

Workaround: preserve original sign-up attribution

Because $source can be overwritten, it's not always reliable for long-term attribution analysis. If knowing a subscriber's original sign-up source is important to your strategy, here's the recommended approach:

Store a custom property at the moment of first opt-in.

For example, create a custom profile property called first_source and set it to the form name or channel value when the subscriber first opts in (via a flow, API call, or form hidden field). Since custom properties are only overwritten when explicitly updated, this value will persist even if $source changes later.

Once set, you can segment on first_source the same way you would on $source:

• Properties about someone > first_source > equals > [value]

This is especially useful for welcome flow personalization, tiered discount strategies, and long-term cohort analysis.

Practical use case: tiered discounts by sign-up source

One powerful application of source-based segmentation is offering different discounts based on where someone signed up. For example:

• Visitors who signed up via a "first-time visitor" popup → receive a 20% off welcome email
• Visitors who signed up via a returning-visitor form → receive a 10% off re-engagement offer
• Past customers who signed up via a loyalty form → receive no discount (they're already engaged)

You can build this by:

1. Creating separate sign-up forms with distinct names for each audience
2. Building segments using $source equals each form name
3. Using those segments as triggers or filters in your welcome flows
4. Sending each segment into a flow branch with the appropriate coupon

This approach lets you avoid over-discounting while still personalizing the subscriber experience from the very first email.

Frequently asked questions

Q: What is the $source property in Klaviyo?
$source is a built-in Klaviyo profile property that records how or where a contact was added to your account — for example, through a specific sign-up form, an API integration, or a manual import. You can use it as a condition in the segment builder to group subscribers by their sign-up origin.

Q: How do I find out what $source values exist in my account?
Open a profile in Klaviyo that you know signed up through a specific channel, scroll to their profile properties, and look for the $source field. The value shown there is what you'll use in your segment condition. Values vary by account and may be text labels (like "Modal") or numeric codes (like -4).

Q: Can I segment by which specific Klaviyo form someone used to sign up?
Yes. Klaviyo sets $source to the name of the sign-up form by default. In the segment builder, use Properties about someone > $source > equals > [Form Name] to isolate subscribers from a specific form. Use OR conditions to include multiple forms in one segment.

Q: Why is my $source segment showing fewer people than expected?
This can happen because $source is overwritten when a profile is updated through a new sign-up action. If a subscriber submitted a second form after their original opt-in, their $source will reflect the most recent form, not the first. Consider using a custom first_source property for more reliable attribution.

Q: Can I use sign-up source to personalize my welcome flow?
Absolutely. Once you've built segments based on $source, you can use those segments as flow filters or triggers to send different welcome emails — including different discount amounts, messaging, or content — based on where each subscriber originally signed up.

Related resources

• Source value reference
• How to segment for form results