Dynamic Number Insertion: How It Works and When to Use It

Dynamic number insertion (DNI) is a small script on your website that shows each visitor a different phone number, depending on how they found you. When someone calls, you know whether they came from a Google ad, a Facebook ad, organic search or an email. DNI swaps the number based on traffic source, which closes the gap between an ad click and a phone call. If your business gets leads by phone, that gap is where your ad budget gets wasted without anyone noticing.

We're a marketing agency in London, Ontario, and we see this problem often with service businesses: the ads "work" on paper, the phone rings, and nobody can say which campaign made it ring. This guide explains how DNI works, where it breaks, what to check in Canada, and whether you need it.

TL;DR

• DNI shows each website visitor a tracking number tied to their traffic source, so every call can be matched to a campaign, ad group or keyword.
• It only tracks web traffic. Print ads, directories and word of mouth need their own static numbers.
• Most failures come from three things: a number pool that's too small, a visitor whose number changes mid-session, and tracking scripts that strip the click ID.
• In Canada, DNI does not replace your obligations under the CRTC's telemarketing rules or privacy law.
• Don't send every call to Google Ads as a conversion. Filter by call length first.

Table of Contents

• What dynamic number insertion actually does
• Do you need it?
• Using DNI with Google Ads
• The three ways DNI quietly breaks
• Canadian rules that still apply
• Choosing a setup: a short checklist
• A worked example
• Our perspective
• Getting your ads and website ready for tracking
• FAQ
• Sources

What dynamic number insertion actually does

Without DNI, every visitor sees the same phone number. You know someone called. You don't know why they picked up the phone.

With DNI, a script runs when the page loads. It checks where the visitor came from, then replaces the number in your header, button or contact page with a tracking number from a pool. That number forwards to your real line. The call tracking system logs which number was dialed, and because that number was shown to one visitor session, it knows the source.

Here's the flow in plain steps:

1. A visitor clicks your Google ad and lands on your site.
2. The script reads the source (and, for Google Ads, the click ID).
3. It shows a tracking number from your pool.
4. The visitor calls that number.
5. The call forwards to your office, and the call record is tied to the original click.

The result is that calls can be attributed to specific campaigns, ad groups or even keywords. That's the same kind of reporting you already get for form fills, applied to the phone.

Static numbers vs. dynamic numbers

A static tracking number is one fixed number for one channel, such as a number printed on a truck wrap or a flyer. A dynamic number changes by visitor. You need both, and they do different jobs.

One limit to remember: DNI only works for web traffic. Mixing static and dynamic numbers without a plan is a common cause of fragmented data, so decide up front which number belongs to which channel.

Do you need it?

Be honest about this before you pay for another tool. DNI earns its keep when:

• You run paid ads and a meaningful share of your leads call instead of filling out a form.
• You spend enough that knowing which campaign produces calls changes where the money goes.
• Your website is the main place people find your number.

It's probably overkill when you get a handful of calls a month, your ads are a small test budget, or most of your business comes by referral. In that case, a single tracked number and a habit of asking "how did you hear about us?" will get you most of the way.

Contractors, clinics, home service companies and other businesses where the customer wants an answer today tend to be phone-heavy. If that's you, our guide to marketing for contractors in Canada and our look at what works for contractor lead generation in Ontario cover the bigger picture around the phone.

Using DNI with Google Ads

This is the setup most readers are after, and where most of the problems show up.

Google's own forwarding numbers

Google Ads has its own tracking numbers for ads and call assets. They're fine for what they're built for, but Google says to use them only within Google Ads campaigns, not on your website, listings or print. Google owns those numbers and can reassign them, which could send a future customer to the wrong business if you printed one elsewhere.

If you only care about Google Ads calls, Google's numbers may be enough. If you also want to compare Google against Facebook, Instagram, organic search and email, you need DNI on your site.

Call length matters more than call count

Google Ads can count a call as a conversion only when it lasts longer than a minimum length you set. Use that. A wrong number, a salesperson, or a hang-up isn't a lead.

The warning here is simple: sending every call to your ad platform as a conversion trains the algorithm on noise rather than high-value leads. Set a threshold that matches a real sales conversation for your business. For a roofer, that may be a couple of minutes. For a restaurant, it may be much shorter. Start with what a real inquiry sounds like and work backward.

Keep the click ID alive

For Google Ads attribution, the tracking script has to capture the GCLID (Google Click ID) and carry it through to the call record. If your landing pages or scripts strip query parameters, the link between click and call is broken for good. This is a website problem as much as a tracking problem. Redirects, form builders and some page builders drop parameters without telling you.

Test it yourself: click one of your own ads, land on the page, then look at the address bar. If the click ID is gone after the first redirect, fix that before you buy any tracking.

The "Unverified phone number" disapproval

Google checks that the phone numbers in call-only ads, call assets and similar placements are in service and relate to the advertised company. Because Google scans your site to confirm your number, a DNI script that swaps it can trigger the disapproval. Google's guidance for this situation includes linking Google Search Console to your Google Ads account, making sure your main business number is hardcoded so it doesn't clash with the script, or using Google's own forwarding numbers if Google Ads is all you track.

If your ads are already running, check your policy status after you install DNI, not a month later.

The three ways DNI quietly breaks

A tracking setup that looks fine in the dashboard can still give you the wrong answers. Check these.

1. Your number pool is too small

DNI hands out numbers from a pool. If you have fewer numbers than visitors on the site at once, a number gets reused too fast, and a new visitor can inherit the session data of the previous one. The same source suggests 5 numbers as a practical starting point, then scaling to your active sessions rather than your average traffic. Many systems report "risky swaps," a signal that pool pressure is high and calls may be misattributed. Watch it, especially after you raise ad spend.

2. The number changes mid-visit

A visitor should see the same number for the whole session. This is the "sticky session" idea: without it, a second swap loses the attribution to the first source. Good setups use cookies or local storage to keep it consistent across pages. Test it by clicking through three or four pages and checking that the number on screen never changes.

3. Nobody reviews the data

DNI isn't set-and-forget. Data quality decides how useful attribution is. Someone needs to listen to a sample of calls, mark which were real leads, and check that the report matches reality. A monthly 30-minute review beats a dashboard nobody opens.

Canadian rules that still apply

DNI is a measurement tool. It doesn't give you permission to do anything you couldn't do before.

In Canada, the CRTC's Unsolicited Telecommunications Rules and Canada's Anti-Spam Legislation still govern marketing communications. Tracking which ad produced an inbound call doesn't override them. The practical points:

• Inbound calls are not telemarketing. A customer who dials your tracking number is calling you. The rules bite when you call or message people for marketing, such as follow-ups to a lead list.
• Keep consent records. If you text or email callers afterward, you need documented consent where the law requires it.
• Respect the National Do Not Call List when you make marketing calls. The CRTC publishes enforcement actions, such as a 2025 notice of violation against a telemarketer, so this isn't theoretical.
• Think about the data you collect. Call recordings, caller numbers and session data are personal information. Read up on Canadian data privacy laws before you turn on recording, and tell callers when they're being recorded.

For anything specific to your business, such as recording calls or running outbound follow-up, talk to a lawyer who handles privacy and telecommunications law in Canada. We're a marketing agency, not your legal counsel.

Choosing a setup: a short checklist

When you compare call tracking tools, whatever the brand, ask these questions. Here is what a good answer sounds like and what should make you walk.

Can I get local Canadian numbers in my area code?

• Good answer: Yes, including 519, 226 or 548 for London and Southwestern Ontario, or 905 and 289 for the GTA and Hamilton areas.
• Walk-away answer: Only toll-free or U.S. numbers. Local callers trust a local number.

How does the pool scale?

• Good answer: You can add numbers as traffic grows and see pool pressure in reporting.
• Walk-away answer: A fixed number of numbers and no visibility.

Does it keep the click ID with the call?

• Good answer: Yes, and it can pass call conversions back to your ad platform with a duration filter.
• Walk-away answer: It only reports counts, with no link to the click.

Can I export my call data?

• Good answer: Yes, in a standard format, at any time.
• Walk-away answer: Your history disappears if you leave. Your data should never be a hostage, not a convenience.

Who owns the numbers?

• Good answer: You can port your main business number out, and tracking numbers are clearly separated from it.
• Walk-away answer: Your main number is locked to the vendor.

One more tip: keep your real business number visible and consistent in your Google Business Profile and directories. DNI belongs on the website and in ad campaigns, not everywhere your number appears.

A worked example

Here's a hypothetical, not a client result. A plumbing company spends money on Google Ads and Facebook ads. Their site shows one number. They get 40 calls in a month and 12 form fills. The form fills carry a source. The calls carry nothing.

After installing DNI with a pool large enough for their peak traffic, the call report might show that most of the calls came from Google search ads, a few from organic search, and almost none from Facebook. They then listen to a sample and find that a chunk of the Google calls were under 30 seconds, mostly wrong numbers and vendors. After setting a call-length threshold, the Google Ads conversions shrink, but they're real. The owner can now decide whether Facebook needs a different offer or less budget.

The numbers above are illustrative. The point is the sequence: capture the source, filter the quality, then change spending. If you want a sense of what budgets look like before you do that, see how much Google Ads costs in Canada and how Google Ads compares with Facebook Ads.

Our perspective

We've seen the same pattern in marketing for local service businesses: the tracking tool isn't the hard part. The hard part is everything around it.

A call tracking number on a site that loads slowly, buries the phone number, or sends ad clicks to a generic home page won't fix itself. Tracking tells you the truth about a weak funnel. It doesn't repair it. So we put things in this order:

1. A site that makes calling easy. Tap-to-call on mobile, the number in view without scrolling, and a page that matches the ad.
2. Ads pointed at the right page. Each campaign lands on a page built for that search or audience.
3. Clean data. Click IDs preserved, call length filtered, spam out.
4. Only then, optimization. Move budget based on calls that turned into work, not calls in general.

We also think owners should be skeptical of any report that treats all calls as equal. A site that never rings the phone is a problem. A site that rings with the wrong calls is a bigger one, because it looks like success.

We work with businesses across multiple industries, not only one type of client, and the same rule holds in each: measure what matters to that business, then act on it. Our focus is London, Ontario, and we also serve businesses in the surrounding Ontario service areas.

— Launch & Found

Getting your ads and website ready for tracking

DNI sits on top of two things we do every day: Google Ads management and website design and build. If you want to check whether your site and campaigns are set up to give you clean call data, we can look at it with you. We also run Facebook and Instagram ads, so you can compare sources side by side.

Our pricing is by custom quote, after we assess whether we're a fit for your business. There are no fixed packages. Contact us for a quote and tell us what you're spending and how your leads arrive. You can also start from our home page to see everything we do.

FAQ

What is a dynamic number?

A dynamic number is a tracking phone number shown to one website visitor for a limited time, instead of the same number appearing to everyone. It forwards to your real line. Because the number was assigned to that visitor's session, the call can be tied back to their traffic source.

Can a phone call be tracked back to an ad?

Yes, if you set it up in advance. Calls can be tied to ads with DNI on your website, with Google's forwarding numbers inside Google Ads, or with static tracking numbers for offline channels. Without one of these, a call arrives with no source attached. Whatever method you use, check what privacy law requires before you record or store call data.

Does DNI track print ads or directory listings?

No. DNI works on web traffic only. For print, signage and directories, use a separate static number for each, and keep your main number consistent in your business listings.

How many tracking numbers do I need?

A commonly cited starting point is 5 numbers in a pool, but the right amount depends on how many people are on your site at the same time, not your monthly average. Watch your tool's reporting for signs that numbers are being reused too quickly, and add numbers if they are.

Sources

• Twilio: What is Dynamic Number Insertion?
• Analytic Call Tracking: Dynamic Number Insertion for Google Ads
• Google Ads Help: Forwarding numbers
• Google Ads Help: Track calls to a phone number on a website
• Google Ads Help: Track calls to a phone number on a website (UK)
• Google Advertising Policies: Unverified phone number
• CallScaler Docs: Number Pools and DNI
• Nimbata: DNI setup
• CRTC: Frequently Asked Questions about Canada's Anti-Spam Legislation
• CRTC: Notice of Violation, Specialty Life Inc.

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