Migrating from HTTP to HTTPS
If you migrate your site from HTTP to HTTPS, Google treats this as a site move with a URL change. This can temporarily affect some of your traffic numbers as described here:
You may experience a temporary fluctuation in site ranking during the move. With any significant change to a site, you may experience ranking fluctuations while Google recrawls and reindexes your site. As a general rule, a medium-sized website can take a few weeks for most pages to move in our index; larger sites can take longer. The speed at which Googlebot and our systems discover and process moved URLs largely depends on the number of URLs and your server speed. Submitting a sitemap can help make the discovery process quicker, and it's fine to move your site in sections.
Beware of common HTTPS/TLS pitfalls that can affect ranking. Review the Common pitfalls section on this page to learn the most common mistakes that we see when sites move from HTTP to HTTPS.
HTTPS sites receive a small ranking boost, but don't expect a visible change. Google uses HTTPS as a positive ranking signal. This signal is one amongst many others, and currently carries less weight than high-quality site content; you should not expect a major SEO advantage for moving to HTTPS in the short term. In the longer term, Google may increase the strength of the HTTPS boost.
Review our G+ post on HTTPS move FAQs. We published a G+ post containing some questions and answers to specific technical questions when moving to HTTPS. You can ask questions there, but please read the existing comments first, as your question may already be answered.
If you have problems, Google Webmaster Central is a great resource. There is plenty of good advice on Google Webmasters and specific cases answered in our user forums. If you can’t find an answer, you can ask a live question to one of our Webmaster Trends Analysts during our Webmaster Central office hours.https://support.google.com/webmasters/answer/6073543