Does CallRail slow down your landing page? A little. Less than most scripts on the page.

What the data shows for CallRail

The numbers here come from third-party-web, an open dataset by Patrick Hulce. It is built from HTTP Archive, which tests millions of pages with Google Lighthouse on mobile settings. Lighthouse records how long each script keeps the browser's main thread busy. The dataset adds that up for each company and divides by the number of pages that use it.

We used third-party-web version 0.30.0, published in September 2026. It holds the HTTP Archive crawl from March 1, 2026. For CallRail it reports:

• Average script execution time: 255 ms per page.
• Usage: 60,963 pages in the crawl.

For context, the same data shows Intercom at 1,433 ms, HubSpot at 1,226 ms, and Google Tag Manager at 1,066 ms. CallTrackingMetrics, another call tracking tool, sits at 282 ms. Call tracking scripts sit on the light end. The full list is in third-party scripts and landing page speed.

What script execution time means for a phone visitor

A phone browser does most of its work in one lane, called the main thread. That lane builds the page and answers taps. While a script runs there, a tap on your "Call now" button waits in line.

Google's Lighthouse docs say it plainly: when the main thread is busy, the page can't respond to user input. Google's Interaction to Next Paint (INP) metric, a Core Web Vital, measures that wait. Google rates INP good at 200 ms or less and poor above 500 ms.

So 255 ms is not nothing. It is time the phone spends on CallRail instead of on your visitor. But one light script rarely sinks a page by itself. The trouble is the stack: call tracking plus chat plus pixels plus a video. Each one adds its own share, and phones add them up.

How to load CallRail the smart way

Most script advice says "wait until the visitor interacts." That works for chat and heatmaps. It is the wrong advice for call tracking.

CallRail has to swap your phone number before the visitor taps it. CallRail also says its Google Ads integration needs visitor tracking for calls to report as conversions. If you hold the script until the first tap, that first tap may dial your plain number. That call never reaches Google Ads as a conversion.

Here is what to do instead:

• Place it where CallRail says. CallRail says its swap script should sit as close as possible to the closing body tag. The page can draw first, and the number still swaps early.
• Test after speed plugins. CallRail says some caching plugins, like WP Rocket, can make its JavaScript snippet fail. Many speed plugins also have settings that hold scripts back. After you change one, check that the number still swaps.
• Use one tool per number. If Google's website call tracking and CallRail both try to change the same number, you load two scripts and get muddy data. Pick one.
• Trim the rest of the stack. Your speed budget is better spent on a heavy chat widget or video embed than on 255 ms of call tracking that pays for itself.

For swap targets, click IDs, and double counting, read CallRail Google Ads integration and your landing page. For the Google side of phone tracking, see Google Ads call tracking.

Check the page after every change

The CallRail script can fall off a page during a template switch or a plugin update. Nobody gets an error. Calls just stop showing up as Google Ads conversions, and the page may get slower at the same time from whatever was added.

ClickMend checks the page your Google Ad sends people to, the final URL. It gives a 0 to 100 score that blends Google PageSpeed Insights performance (40%), Core Web Vitals (25%), SEO basics (20%), best practices (10%), and accessibility (5%). It names unused JavaScript and other slow parts, so you can see which scripts weigh the page down. It also checks the Google Ads conversion tag: is it there, did it load, is the ID a placeholder, is the conversion linker off.

ClickMend does not read your CallRail settings. Test the swap yourself in a private window, as CallRail suggests. Then scan the landing page free, 2 scans a week, no card. Paid plans add weekly monitoring with alerts when a page gets worse. For more on page speed, see landing page speed test.

Frequently asked questions