[Case Study] Slow Shopping Cart Pages Are Killing Conversions. An Optimized Page Got a 66% Conversion Lift!

You’ve just invested a gazillion dollars in getting your site ready for the holidays, but 1 out of 5 of your customers will abandon their shopping cart if your pages are too slow. Is your checkout process fast enough, or are you losing your shoppers at the final point of sale? And what can you do about it now that the holiday shopping season is breathing directly down your neck?

The total cost of abandoned shopping carts for online retailers has been estimated to be over $18 billion a year. 18% of those who abandon carts say the reason was slow page load. That’s more than $3 billion in lost sales due to poor performance. This problem is too great to ignore.*

Shopping cart abandonment has increased, not decreased, over the years

According to recent data from Forrester, only 3 out of 10 shopping carts make it through the checkout process. This is interesting in its own right, but what’s equally interesting is the fact that shopping cart abandonment has increased, not decreased, over the past five years.

This flies in the face of a major assumption that many people — including online retailers — make: that online shoppers have become more sophisticated over the years, meaning they understand the ins and outs of the checkout process and are willing to roll with the fact that each stage of the process takes time. Clearly, this isn’t the case.

Many online sellers have gotten smart about making their sites faster, and they’ve focused a lot of energy on accelerating landing pages and product pages. However, they’ve neglected their checkout process, and they’re losing sales as a result. As I mentioned at the top of this post, 1 out of 5 shoppers will abandon their loaded shopping cart if they perceive the pages as being too slow.

Case study: Tracking abandonment rate throughout a transaction

This summer, my company, Strangeloop, worked with a customer who wanted to experiment with the impact of page slowdown on a 5-step transaction. We did a split test in which we divided traffic into three groups and delivered different load times to each.

For group #1, we delivered a fully optimized set of pages, which established a baseline optimal conversion rate. As this video shows, at the end of all 5 steps, one-third of all users had completed the transaction:

Now, we know from past experience that slowing down landing pages affects conversions, but we wanted to quantify that in this instance. So for group #2, we introduced a 2-second delay to the first page in the transaction. As you can see, conversions dropped by 60%, as only 2 out of 15 users completed the transaction:

No big surprises so far. But we wanted to test something new. We wanted to see the impact of slowing down a page mid-way through a transaction. So for group #3, we introduced a 2-second slowdown to the third page in the flow. Bear in mind that these are people who’ve already engaged with a process. They’re halfway through, and would seem to be committed. Despite this, we found that the dropout rate was still dramatic at this stage, and by the end, only 3 out of 15 users had completed the transaction:

To summarize: You can spend all kinds of ad dollars getting people to your site. You can invest in SEO to get people to your product pages. You can offer the most competitive prices and free shipping to tempt people to load up their shopping carts. But if you can’t make the checkout process fast on every single page of the process, you’re going to lose those hard-earned visitors.

How fast should pages in a checkout process be?

In lab test after lab test, going back as far as Robert B. Miller’s classic 1968 paper “Response Time in Man-Computer Conversational Transactions“, studies have found that people are — and always have been — most comfortable, most efficient, and most productive with response times of less than 2 seconds. If your checkout pages take longer than that, you need to figure out why.

4 common shopping cart performance culprits

1. Too many pages in the checkout process

There’s a reason why companies like Amazon have made it a priority to allow one-click checkout for customers who want to hustle through the purchasing process. They know that each stage in the checkout process is an invitation for attrition. And with 37% of shoppers saying they plan to buy via mobile this holiday season, it’s more important than ever to make the checkout process as simple and streamlined as possible.


The checkout process has to be secure, but this security comes with a performance price tag. All that handshaking, encrypting, and decrypting takes time and can bog down page load. Security is a big issue — too big to be summed up in a single paragraph — but suffice it to say that if you want to make your checkout process faster, you really need to take a deep look at how your site handles security. One quick tip I can give now is that you should enable your HTTPS content to be cached by the browser, which will help your checkout pages render somewhat faster. There’s a bit of a myth that HTTPS content can’t be cached, but in actuality this is controllable with response headers, just like HTTP content.

3. Too many page objects

Enabling browser caching will help with this problem, but you should also take a hard look at your checkout pages and get rid of extraneous images and other large files. For one thing, they’re unnecessary and distracting when you’re trying to get shoppers to focus on completing a simple task. And for another thing, they eat up bandwidth.

4. Third-party service calls

If your site is using third-party services such as address validation, credit card authorization, and analytics, you need to make sure these services are performing quickly and reliably during checkout. Do you know what kind of service-level agreement you have with your service providers? What kind of monitoring and reporting do they offer? You need to have full transparency into their performance so that you can make or request fixes.

These tips are a start. If you remember only three things from this post, those things should be:

  1. Online shoppers are never going to “learn” to be patient with slow pages.
  2. To maximize sales, every single page of a transaction — from landing page through to order confirmation page — needs to be fast.
  3. How fast? Less than 2 seconds.

*If you’re wondering how much cart abandonment is costing your company, shopping cart solutions provider Listrak has created an online calculator that can give you a ballpark idea.

— Joshua Bixby

default author image
About Joshua Bixby
Joshua Bixby is president of Strangeloop, a company that provides website acceleration solutions to companies like Visa, Petco, Travelocity and OReilly Media. Joshua also maintains the blog Web Performance Today, which explores issues and ideas about site speed, user behavior, and website optimization.
» More blog posts by Joshua Bixby