I measured 49 of my own WordPress builds against 20 theme demos. The demos lost.

A recent study compares the performance of 49 custom-built WordPress sites against 20 popular theme demos. The results show that the custom-developed sites outperformed the demos significantly.

The comparison group consisted of 38 optimised custom sites with an average PSI mobile score of 89.9, and 11 unoptimised custom sites averaging 65.2. In contrast, the 20 demos scored an average of 53.9 on mobile. None of the demos reached a score of 90 or above, while half of the custom optimised sites achieved this benchmark.

Core Web Vitals, which measure LCP (Largest Contentful Paint), CLS (Cumulative Layout Shift), and INP (Interaction to Next Paint), further demonstrated the performance gap. 45% of custom optimised sites passed the tests, compared to just 10% of the demos. CLS was particularly low for custom sites, with 28 out of 38 recording a score of 0.00.

Plugin count was found to be a key factor in performance, with custom sites averaging 9.3 plugins, while the demos averaged 13.6. One poorly optimised custom site, with 38 plugins and a 10.5 second LCP, proved that even custom development isn't a cure-all.

The study also showed that larger sites, such as e-commerce catalogues, news archives, and construction product sites, still maintained good performance despite the scale of the site. Maintenance costs for custom builds were minimal, averaging around 1-2 hours per year, while template sites required around 8 hours per year for fixes. The most common issue with template sites was hosting updates causing compatibility problems with older builder code.

Overall, this research suggests that custom WordPress development offers superior performance and maintenance costs compared to using theme demos or builders, making it a conscious trade-off worth considering for businesses seeking a competitive edge.