The Back Story

I used to manage a website for a paid monthly subscription service.
Amongst others, My main responsibility was CRO (Conversion Rate Optimization).
I’d rather not state the service’s name since the data i am about to show might be a bit sensitive and it doesn’t contribute anything to the point I’m trying to make.

So, as I was saying – We are talking about a monthly subscription service who main source of acquisition is the website in question.
Most of our paid media and organic search landed the users on a homepage / landing page whose main purpose was to educate the users about the product and motivating them to signup for a monthly subscription.

Almost none of the traffic was targeted towards the signup page.
That’s because i thought it’s important the users are able to get all the info about the product and the offering before deciding wether or not they want to signup.

After trying various creatives and offerings on the landing page I’ve the decided to take a look at the time it takes the home page load and if and how it affects the conversion rate from landing on the homepage to signing up for the monthly service.

Soon enough I’ve noticed that the time it takes our homepage to load differs from day to day. Mainly due to server load but also because of content on the page (that was constantly changing), the users network speed, and more…

For instance, More heavy weight, high quality images equal longer loading time and more work load to the server itself which causes more traffic to generate longer server response times and in turn longer loading times for the end user.

I’ve also noticed that the page loading speed had a direct and obvious correlation to page’s bounce rate.

What is bounce rate?

Google defines bounce rate as:

The percentage of visitors to a particular website who navigate away from the site after viewing only one page and without performing any action

Google Analytics Help Center

For instance, say you have a landing page with a button in the banner that says “Click here for more info” and when someone clicks that button the page scrolls to another section on the same page.

Assuming that the button click is tagged with a Google Analytics event (and it should be) and that event is not defined as a “Non Interaction Event” –
The click on that button is an action that the user performed and thus, The session will not be counted as a bounced session.

For that reason, I would define bounce rate of a page as “the percentage of sessions that viewed the page and left without making any other actions or viewing other pages on the site”.

Why you should care about bounce rate

A high bounce rate means low engagement from users and thus poor performance business-wise.
As I Mentioned before, Bounce rate has a massive and direct impact on conversion rate, And so the first step in improving the conversion rate is keeping users on the page. AKA lowering the bounce rate as much as possible.

A webpage’s Bounce Rate metric is also a major factor in Google’s page ranking algorithm.
A low bounce rate would also provide a great deal of help to rank the page higher on Google’s organic search.

Actual Data – Page load time vs. Bounce rate

Below is a graph that shows the home page’s bounce rate vs page load time over a 50 day period.

Page speed vs. Bounce rate over time
Page speed vs. Bounce rate over time

Doesn’t take a rocket scientist to notice that at the days where the average page load time was high the bounce rate rose with it in distinct correlation.
As mentioned before – a high bounce rate would almost always lead to a lower conversion rate and that really hits us where it hurts.

Actual Data – Page load time vs. Conversion rate

Below is a graph that shows the home page’s conversion rate vs page load time over a 50 day period.

Page speed vs. Conversion rate over time
Page speed vs. Conversion rate over time

Again we see a distinct correlation.
This time it’s reversed, When the homepage took longer to load = Less users converted.
Take a look at day #38 for instance.
On that day there was a significant increase in the amount of traffic to the page which added to servers workload and caused the average page load time to rise from around 4 seconds on a regular day to about 9 seconds.
At a first glance this might not sound like a really big deal but when you take a closer look you can clearly see that those 5 extra seconds of page load time cost us almost 40% of our conversion rate.

How does Google Analytics measure page speed metrics?

Google analytics has 7 different metrics to measure page load performance:

  1. Avg. Redirection Time
    Only relevant if there are redirects from the requested page to a different URL. If so, this metric will hold the time it took since the user requested the page until he was redirected to the new page.
  2. Avg. Domain Lookup Time
    The time it took the browser to resolve the URL into an IP address. This value could be bigger if your page includes content from multiple domains.
  3. Avg. Server Connection Time
    The time it took to establish connection to the web server.
  4. Avg. Server Response Time
    The time the server takes to respond to a user request, including the network time from user’s location to your server.
  5. Avg. Document Interactive Time
    The time that’s passed since the user requested the page (e.g. clicked on a link to page) until the page became interactive (e.g. the user can scroll and click stuff).
    This value is an important one, As it states the amount of time the user had to wait before they can interact with the page
    (aggregates all previous metrics up to this point in time)
  6. Avg. Document Content Loaded Time
    The time that’s passed since the user requested the page (e.g. clicked on a link to page) until the users’ browser took to parse the document and execute deferred and parser-inserted scripts.
    This is when jQuery fires the “ready” event.
    (aggregates all previous metrics upto this point in time)
  7. Avg. Page Download Time
    The amount of time that has passed since the document has finished downloading until all external resources (images, stylesheets, etc…) have finished downloading.
  8. Avg. Page Load Time
    The time that’s passed since the user first requested the page until and the page fully loaded.
    (aggregates all previous metrics upto this point in time)
Google Analytics page speed metrics timeline
Google Analytics page speed metrics timeline

Summary & Conclusions

Page load times have a direct impact on conversion rates.
Even the slightest fluctuation in the time it takes to load a page can (and probably will) cause a dramatic change in conversion rates.
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If we want to maximize conversions It’s of outmost importance to take all measures to decrease the time it takes a page to load to the bare minimum.