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Yes there can be big impacts, as template changes may result in any of the following changes: Design and UX Site Architecture Internal Linking Page Speed Other possible inconsistencies between themes, depending on your WordPress setup in general (title tags, structured data, etc) In general, to mitigate against these, I would do the following: Design and UX - at minimum take a 'gut check' and be sure the new theme is a design and UX improvement - ie: is content still above the fold? Are there any weird scrolling issues (I see this sometimes with themes that try to be too fancy), are the menus still easy to navigate? Architecture - make sure the new theme doesn't break anything like your URL structure, or pagination links to archive pages etc. Internal linking - aim to keep your menus (main nav, drop downs, footer, sidebars) exactly the same at least for now - if your footer nav has links to important pages for example and those links go away, this might hurt the performance of those pages. Page Speed - as Donald astutely noted, make sure the new theme is at least the same in page speed, or better an improvement. You can use a few tools like WebPageTest or GTMetrix to test. Other - also as noted, try to get your SEO settings situated correctly before making the switch, and use the Yoast plugin. Then when you switch your theme, be sure the Yoast plugin settings are still primary and your new theme has not overridden anything. Hope that helps! -Dan