This question is frequently asked by people who are new to WordPress or are experimenting with Free WordPress themes. The answer is ‘It Depends’. There are certain factors responsible for SEO. You can achieve higher ranks as well by having a properly coded theme or your rankings may suffer heavily. At first, your ranking will definitely suffer some loss but if you are having the following aspects ready with your new theme, you will soon recover your rankings. May be you will now have better rankings this time. There are certain factors to be taken into account in your quest for best WordPress themes, so that your On-Page SEO should not suffer.
• W3C validation Test
Google ranks the themes higher which have passed the w3c (World Wide Web consortium) HTML validation test passed. It greatly affects the SERPs as Google and other search engines read the text in a sequential manner. Make sure the order of HTML is perfect. Check out the HTML source (you can easily get that by right clicking on the browser and clicking the view page source option) of your theme. Make sure that the titles or headings (h1, h2) followed in your new theme are standardized. This will also make your switching easier. If your new theme is constructed using schema.org, then surely it is going to give an immense boost to your Search engine rankings.
• SEO Plugin
This is another major factor contributing in SEO rankings. If you are using a theme which has in-built SEO facility, then you are definitely going to lose your SEO rankings. I would recommend you to use a SEO plugin instead so as to keep your SEO intact even after changing your theme for the best WordPress theme. If you don’t have an SEO plugin, then make sure you have one and take a complete backup of the SEO settings in your plugin and then start the swapping process. After swapping the theme, it is advisable to re-check the integrity of the meta data including the meta descriptions provided are intact and are not missing. The professionals recommend using a SEO plugin with the basic WordPress theme so that you do not lose any rankings, irrespective of the swapping in the theme.
• Link Structure
After shifting to new theme, make sure that the Permalinks are the same else you have to pay heavily in terms of SEO. If any error occurs fix it or provide a 301 redirection URL else the visitor will face a 404 error which indeed is very frustrating. Also, recheck that all the links, tags and categories are working perfectly. All the links should be perfect and pointing to the page where they are intended to. Google bots or crawlers visit all the links to make up the SEO of the page.
• Loading Speed of the theme
There are certain Best WordPress themes which load the header first, then menus and then the main content. All the search engines prefer the themes with low loading time. The more the speedier the website is the higher is the ranking. Make sure that the theme you are selecting is not only HTML validated but also has low loading time. Go for a demo before actually shifting your site.
There are other factors as well like checking for responsiveness of a theme so that you equally draw good traffic from the mobile users. Another can be browser compatibility. And one main thing, just go for the reviews and ratings before deciding your choice. Or at least read the testimonials by users who are already using that theme. So, I think now you are good to go for selecting you new theme and can have your SEO intact with the new theme as well.