Understand how Meta attributes events to your ad campaigns
Meta relies on multiple signals to attribute web events (such as purchases, leads, or page views) back to ads. The most important of these signals is the fbclid (Facebook Click ID), but cookies and user data can also be used when fbclid is missing.
This guide explains how each identifier works, why fbclid matters, and what happens when it is not present.
What is fbclid?
fbclid stands for Facebook Click ID.
It is automatically added to the URL when someone clicks on a Meta ad.
fbclid provides a deterministic link between a web event and a specific ad click.
When an event is sent with fbclid, Meta can directly tie it back to the exact campaign and ad that drove the click.
Why it matters: fbclid is Meta’s strongest attribution signal. Without it, attribution becomes less reliable.
Can Events be Atttributed Without fbclid?
If an event is sent without fbclid, Meta may still attribute it using other signals, but accuracy drops. Attribution can rely on:
fbc Cookie (
_fbc)Stores the fbclid from the first click.
Allows Meta to deterministically connect later events to the same ad click, as long as the attribution window is still valid.
fbp Cookie (
_fbp)Identifies the browser or device.
On its own, fbp cannot guarantee attribution, but it helps Meta connect activity to a user’s ad history.
User Data Parameters (via Conversions API)
Includes identifiers like email, phone number, IP address, and user agent.
Meta hashes these values and attempts to match them to a Facebook or Instagram account.
If that account clicked or viewed an ad within the attribution window, Meta can attribute the event.
If none of these identifiers are available, Meta often marks the event as unmatched or unattributed, meaning it will not be tied to a campaign.
What are the Meta Attribution Windows?
Meta uses attribution windows to decide whether a conversion should be credited to an ad. The default setting is:
7-day click: A conversion counts if it happened within 7 days of clicking an ad.
1-day view: A conversion counts if it happened within 1 day of viewing (but not clicking) an ad, if view-through attribution is enabled.
Example: If a user clicks an ad on Monday and makes a purchase on Friday, that purchase will be attributed. If the purchase happens 10 days later, it will not.
What Happens If There's No fbclid?
If there's no fbclid in an event sent to Meta, Meta may still attribute that event to a specific ad campaign but its less reliable and may even not be matched to a campaign.
With PixelFlow, its possible to not send any events back to Meta if there's no fbclid using the Advanced Blocking Rules but its generally not advised for most users as there are only some rare edge cases where this makes sense as sending all of your traffic to Meta helps with Meta's learning phase and finding new customers based on existing events from your website.
With fbclid: Events are tied directly to the ad click, attribution is accurate.
Without fbclid: Attribution depends on cookies and user data. Meta can still attribute conversions, but the process is less reliable.
No identifiers at all: Events may be unmatched or unattributed, reducing reported campaign results.
How Does Meta Attribute Events on your Website to Ad Campaigns?
fbclid is the most direct way to attribute a conversion to an ad.
If fbclid is missing, fbc, fbp, and user data can still help, but attribution accuracy decreases.
Events outside the attribution window will not be credited, even if fbclid is present.
Using the Conversions API (CAPI) improves attribution accuracy by sending additional identifiers server-side.
In summary, without fbclid, Meta can still attribute conversions, but results may look weaker than they actually are. For the best accuracy, PixelFlow with the Conversions API to send complete parameter data.