What is dynamic number insertion (DNI)? A UK setup guide

What is dynamic number insertion and how does it work in the UK?

Dynamic number insertion (DNI) is the technique that changes the phone number displayed on a website automatically, based on how each individual visitor arrived. A visitor coming from a Google Ads click sees one number; a visitor arriving from an organic search result sees your normal published number. Both numbers ring the same phones, and the caller notices nothing.

The mechanism is a small piece of JavaScript and a pool of tracking numbers. When someone lands on your site, the script reads the referral data attached to that visit — the source, the campaign, the keyword, the Google click identifier — and reserves a number from the pool for the length of their session. If they ring it, the platform looks up which session held that number and attaches the full campaign detail to the call record.

That is the whole trick. Static tracking numbers can tell you a channel produced calls. DNI tells you which keyword produced them, because the assignment happens per visit rather than per channel.

How do I set up dynamic number insertion with Google Ads in the UK?

Setting up DNI with Google Ads takes four steps and usually under an hour.

1. Connect the ad account. Link your Google Ads account to the call tracking platform so it can read campaign, ad group and keyword data, and match the click identifier that Google appends to your landing page URLs.

2. Choose the number pool. You need enough tracking numbers that two simultaneous ad visitors never share one, or attribution collapses. A rough rule is one number per concurrent ad session at your busiest hour — most UK SMEs sit comfortably in single figures, high-spend accounts need more.

3. Install the script. One line of code goes on every page, ideally through your existing tag manager. It should replace numbers by CSS class or by matching the number string, so a number added to a new page later is picked up without another deployment.

4. Set your swap rules. Decide who sees a tracked number. The standard setup swaps only for paid visitors and leaves organic, direct and referral traffic on your published number — which keeps your public NAP details untouched.

Then test it properly before you trust the reporting. Click one of your own ads, check the number on the page has changed, ring it, and confirm the call appears in the dashboard against the right keyword.

Does dynamic number insertion affect local SEO and Google Business Profile?

Dynamic number insertion does not damage local SEO when it is configured to swap only for paid visitors. Google's local ranking signals depend on NAP consistency — your name, address and phone number matching across your website, your Google Business Profile and third-party directories. A correctly scoped DNI setup leaves the published number in place for organic visitors, in your schema markup, in your footer and in your citations, so the consistency Google checks is never broken.

It goes wrong in two specific ways, both avoidable. The first is swapping numbers for organic traffic as well as paid, which puts a rotating number in front of the crawler. The second is letting the script replace the number inside your LocalBusiness structured data or your Google Business Profile listing. Keep the swap to visible ad-visitor numbers only, and leave schema and citations alone.

What are the GDPR considerations for dynamic number insertion in the UK?

DNI processes personal data, so a UK business using it needs to handle it under UK GDPR and the Data Protection Act 2018 like any other tracking. Three things are worth being deliberate about.

Cookies and consent. DNI stores an identifier on the visitor's device to hold their number for the session. Under PECR, non-essential storage requires consent, so the script normally belongs in the same consent category as your analytics rather than firing before the banner is answered.

Call recording. Tracking a call and recording it are separate decisions. If you record, callers must be told at the start of the call and you need a lawful basis, defined retention and restricted access. A recorded greeting carrying the notice is the simplest way to handle the first part.

Your privacy notice. Say that calls may be recorded and that phone numbers displayed on the site are used to attribute enquiries to advertising. It is a short paragraph, and it is the thing most often missing.

This is general information rather than legal advice — check your own position with whoever handles data protection for your business.

Is DNI worth it for a small UK business?

Dynamic number insertion earns its place when the phone is genuinely how you sell and you are paying for the traffic producing those calls. Solicitors, clinics, dentists, garages, trades and estate agents fit that shape: high value per enquiry, high phone intent, and enough ad spend that guessing which keywords work is expensive.

It is harder to justify below a few hundred pounds a month in advertising, or if enquiries arrive almost entirely by form. The question DNI answers — which keyword produced that call — has to be worth more than the platform costs to answer it.

CallTrace includes DNI on both plans: £99 per month for Call Intelligence, £199 with Live Coach. Monthly rolling, priced in pounds, and the setup above is what we do with you rather than hand you as a task.