# fbc parameter builder · Postback Report > Source: https://postbackreport.cc/best/fbc-builder-turn-an-fbclid-into-the-fbc-value-the-conversions-api-expects ## Build the fbc string A server Purchase matches the ad when user\_data.fbc is the formatted ClickID. The fbclid in the URL is the last piece of that value. Copy fbclid from the URL that still contains it. The [redirect guide](/compare/fbclid-parameter) shows the hop that drops it, and formatting comes after that. **Disclosure:**We may earn a commission when you buy through links on this page. It never affects our rankings. [How we research](/methodology). Click id Landing URL or fbclid Paste the full address or the token alone, and the token keeps the casing you paste. Domain index Use 1 From the hostname Choose 0, 1, or 2 A server build with no saved \_fbc cookie uses 1, which is the default here. Cookie domain 0, one-label domain 1, two-label domain 2, a www hostname Click time Now A time I enter Now uses the millisecond clock at the moment you build the string, down to that instant. When you first saw the click Compare Existing \_fbc, optional Paste a cookie you already have, and the form only compares it with the string it builds. Build the fbc The calculation stays in this browser, on the machine where you opened the form. After you submit, the formatted string, the index, and the time show up here. ### How the fbc parameter is set [Meta's parameter page](https://developers.facebook.com/docs/marketing-api/conversions-api/parameters/fbp-and-fbc/) says the formatted ClickID must be version, subdomainIndex, creationTime, and the fbclid, with a dot between each piece, and the version is always the letters fb. subdomainIndex follows the cookie domain. In the examples on that page, com is 0, example.com is 1, and www.example.com is 2\. A server build that never saved an \_fbc cookie uses 1, so set the domain index to 1 in that case, and counting the hostname works the same way: one label is 0, two labels are 1, and three labels are 2\. You pick the index yourself when a hostname has four or more labels, because those examples stop at a www host. creationTime is the UNIX time in milliseconds when \_fbc was stored, or when you first saw the fbclid if you do not save the cookie. When the browser did save \_fbc, that cookie is already the formatted value, and the compare field checks a paste against a fresh build. The fbclid segment preserves the casing Meta used in the URL, and changing that case breaks the match. ### The string in Meta's example fb.1.1554763741205.AbCdEfGhIjKlMnOpQrStUvWxYz1234567890 That is the value from the same documentation page: fb is the version and 1 is the domain index, while 1554763741205 is the creation time, and you should send all thirteen digits because the same moment in seconds would drop the last three. The last segment is the sample token, with its capitals kept as written. [Meta's parameter builder library](https://developers.facebook.com/docs/marketing-api/conversions-api/parameter-builder-feature-library) documents this same order, before any optional appendix, and the form stops after the fbclid. ### The field in the payload The click id belongs in fbc. A payload that puts fbclid on its own inside user\_data comes back with an unexpected-key error on that field. ### After the string is ready If a browser pixel also fires, both events need the same event id. The [deduplication guide](/compare/facebook-conversion-api-deduplication) shows how to pair them. What each path sends is in the [pixel and Conversions API guide](/compare/facebook-pixel-vs-conversion-api). When the sale arrives on a network postback, the [offline guide](/compare/meta-offline-conversions-affiliate-postback) covers the Meta upload. The [postback URL builder](/best/postback-url-builder-the-network-postback-for-your-tracker-with-click-id-and-pay) assembles the network address, with the click id and the payout macro. The [late approval checker](/best/late-approval-checker-can-meta-and-google-still-take-the-network-sale) compares the click day with the day the sale becomes payable. On Google, that click id is called gclid, and the [tracking template builder](/best/google-ads-tracking-template-builder-pass-the-gclid-to-your-affiliate-tracker) places it on the URL a tracker reads. ### My take I would start by pasting the full URL, because that paste has both the token and the host, and I would judge the finished string by a thirteen-digit time and by capitals that still match the token. A raw fbclid field on user\_data is what I would skip, since the click id already sits inside fbc. ### When ElasticFunnels builds it ElasticFunnels is a funnel platform for teams that run paid traffic. It builds the pages, split-tests variants under one URL, and hosts the checkout, with the click and the order on the same record. On a hosted page, when there is no \_fbc cookie, ElasticFunnels builds fbc from the fbclid in the landing URL. Its [Meta Ads page](https://elasticfunnels.io/integrations/meta-ads) says those checkout sales go to Meta as server-side Purchase events with fbc and fbp in the payload. ElasticFunnels is newer than the platforms it competes with, and there is very little independent third-party review coverage to check that fbc build against. Until you run real volume through it, you are largely taking the vendor's word for the server Purchase. It has been on the market since 2023, which is why those outside write-ups are still thin. The pages, the same-URL test, and the checkout are part of the same account. The [ElasticFunnels review](/reviews/elasticfunnels) goes through the rest of the platform. ### Questions How is fbc different from fbclid? fbclid is the token Meta appends on the ad click. fbc is the server value, with the version, the domain index, and the time written in front of that token. Which domain index should I use? Use 1 when you format the click on the server and you never stored the cookie. Use 0 for a one-label cookie domain, and 2 when the cookie domain has a www label. Should I send the raw fbclid? Put the token inside fbc, because a payload that adds fbclid as its own user\_data field fails validation. Where does the creation time come from? If a cookie was saved, the middle number is that save time in the long digit form from the example above, and if you never saved one, it is the time the token first arrived, in that same form. What does the \_fbc cookie hold? The cookie is the formatted value, so paste one you already have into the compare field, and a match means the fresh build equals it, while a missing cookie means you build from the URL that still has the token. ### Changelog 22 October 2026. First version of the formatter. ### What we read * [Meta fbp and fbc parameters](https://developers.facebook.com/docs/marketing-api/conversions-api/parameters/fbp-and-fbc/) * [Meta parameter builder library](https://developers.facebook.com/docs/marketing-api/conversions-api/parameter-builder-feature-library) * [Where a redirect drops fbclid](/compare/fbclid-parameter) * [ElasticFunnels Meta Ads](https://elasticfunnels.io/integrations/meta-ads) ### Related reading * [Best affiliate trackers](/best) * [The redirect that drops fbclid](/compare/fbclid-parameter) * [Deduplicating pixel and server events](/compare/facebook-conversion-api-deduplication) * [Facebook pixel vs Conversions API](/compare/facebook-pixel-vs-conversion-api) * [Meta offline conversions from an affiliate postback](/compare/meta-offline-conversions-affiliate-postback) * [Late approval checker](/best/late-approval-checker-can-meta-and-google-still-take-the-network-sale) * [Google Ads tracking template builder](/best/google-ads-tracking-template-builder-pass-the-gclid-to-your-affiliate-tracker) * [Postback URL builder](/best/postback-url-builder-the-network-postback-for-your-tracker-with-click-id-and-pay) * [ElasticFunnels review](/reviews/elasticfunnels) Written by Nadia Lindqvist Affiliate tracking Nadia covers affiliate tracking software for people who buy Meta and Google traffic. She reads vendor pricing pages, documentation and long-term user reports, and she writes about which tracker fits a given buyer. [nadial@postbackreport.cc](mailto:nadial@postbackreport.cc) Last checked 2026-10-22 --- [ Postback Report ](/) Postback Report ranks affiliate tracking software for media buyers running Meta and Google direct response, judged on postbacks, cost, and the Conversions API. [Contact](/contact) Postback Report We may earn a commission when you buy through links on this page. It never affects our rankings. © 2026 Postback Report. Independent and reader-supported.