For the last few years, effectively zero.<p><a href="https:&#x2F;&#x2F;istlsfastyet.com&#x2F;" rel="nofollow">https:&#x2F;&#x2F;istlsfastyet.com&#x2F;</a><p><a href="https:&#x2F;&#x2F;www.maxcdn.com&#x2F;blog&#x2F;ssl-performance-myth&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.maxcdn.com&#x2F;blog&#x2F;ssl-performance-myth&#x2F;</a><p><a href="https:&#x2F;&#x2F;www.imperialviolet.org&#x2F;2010&#x2F;06&#x2F;25&#x2F;overclocking-ssl.html" rel="nofollow">https:&#x2F;&#x2F;www.imperialviolet.org&#x2F;2010&#x2F;06&#x2F;25&#x2F;overclocking-ssl.h...</a><p>Not to mention that if you use CloudFlare just to get a free SSL certificate out of them, you&#x27;re also getting a CDN, so the performance overhead is <i>negative</i>.