Dynamic number insertion, explained
· CallRadar Team
Dynamic number insertion (DNI) is the piece of call tracking that people find hardest to believe: the phone number on your website is different for different visitors, and that is what makes call attribution work.
How the swap happens
You add one script tag to your site. When a page loads, the script looks at how the visitor arrived - the referrer, the UTM parameters, the ad click ID - and replaces your default phone number with a tracking number reserved for that source, or for that visitor’s session.
The swap happens before the visitor reads the page, so nobody sees a number change. Your real number stays in place for anyone with the script blocked, which means you never lose a call to the tracking itself.
What it buys you
Session-level DNI ties a call to a specific visit: the campaign, the keyword, the landing page, and the pages viewed before the call. That is the difference between “the phone rang eight times today” and “Tuesday’s calls came from the emergency keywords, not the brand ones.”
The two mistakes that break it
Hard-coding the number in images. The script can only swap text. If your number lives in a banner image, it cannot be tracked - keep it in HTML.
Inconsistent formatting. The script finds your number by matching it. If the site shows it five ways, list every variant in your settings, or standardise the formatting once.
Set up correctly, DNI is invisible to visitors and takes about ten minutes. It is the highest-leverage ten minutes in call measurement.
