When planning a website, marketers focus on functionalities, user experience (UX) and appearance to reflect the desired brand image. And rightly so. But it is worth remembering that UX, the subjective impression of the user, and finally – conversions and the implementation of business plans – are influenced by the speed of the website. A lot. The problem is especially relevant to e-commerce. According to Bain & Co. calculations quoted by IBM, A 5% reduction in customer outflow caused by negative UX could result in a 25-125% increase in profitability e-commerce, depending on the industry. Each user has a different tolerance for long page load times. But a number of observations confirm that it is clear the limit is 4 seconds – at least half of us will not hurt anymore. Also, most conversions take place on pages that take up to 4 seconds to load. Shortening the page loading time always results in a significant increase in the conversion rate and profitability of the store – both for a global giant and a large specialist store. The matter is even more important in connection with the popularization of browsing on mobile devices. 2 years ago in the USA 4 out of 10 users left mobile pages that could not be loaded within 3 seconds. Thus, the expectations of the user of a mobile device are even higher than that of a “desktop”. A complex Radware study found that free mobile sites caused a significant increase in frustration and decreased engagement during a visit. What’s more – this negative experience also affects the user’s future relationship with the brand: It lowers the willingness to buy, and even builds negative connotations brands with features like “boring”, “inelegant”, “clumsy”. So the performance of the website can significantly influence the perception of the brand. So we know that it is worth investing. Another question arises – how much and what, because it is known that the marginal utility of each investment is decreasing. Therefore, how much faster page loading has an effect on business results? Experts from Microsoft and Google say about 250 milliseconds, that is 1/4 of a second. The psychology of perception knows this value – 250-350 ms is the average time of eyesight fixation. Because our eyesight works a bit like a radar, in 2 modes: searching and tracking. In Search mode, the moving eyeballs stop for 1 / 4-1 / 3 seconds on environmental objects so that the brain, not yet consciously, judges whether or not an object is worth tracking – this is what is called fixation. This means that the distraction and impatience of the “typical internet user” have already reached the biological limit. And so is the race for his wallet. I remember when the first WYSIWYG page editors appeared. Many people said then: why do we need programmers, if you can put together a page in Pajączek or even Powerpoint yourself. One of the arguments for a professional approach was the redundant code generated by these editors. Its processing took time for computers, and most of all – it consumed the resources of Internet connections. Back in the days when the dial-up modem was king, it was a really important argument. I think history has come full circle. Today, anyone can build a very nice and rich website using, for example, WordPress, hundreds of templates and thousands of plugins. However, the growing requirements as to the usability of websites mean that the modern website can also “walk” slowly. And the problem is not so much in the link resources as in the user’s attention resources. That’s why professional website coding is a worthwhile investment.