Can a website’s dowtime affect the SERP?

I noticed this question is being asked pretty frequently in webmasters forums. People lost their ranking as their server went down and the website wasn’t accessible through internet. Does this really affect the ranking? The answer is yes, it does.

Well, to be very frank, I have a firsthand experience of this. One of my clients has a pretty large forum which was getting well over 35,000 unique visitors per day with 350,000 pages indexed. His server was not being able to cope up with the load he decided to upgrade it for good. The old server was crashed suddenly on a Friday evening and after a successful server upgrade the forum was up again on Tuesday. It was down for 90 hours. He checked the indexed pages and it was only 29,000 by that time. Google started to re index them again but he is yet to get back the ranks.

That story clearly shows that downtime do effect the search engine rankings of a website. Let’s see how and why..

• If your site was down for a very little time, for example 15 minutes, and crawlers didn’t crawl your pages meantime, you will not face any problems. If crawlers came to visit your site meantime and the site wasn’t reachable, they will try it again after a few minutes. This is normal and search engines understand that it may happen due to common issues like network congestion.
• If your site was down for a day or two, search engines will deindex the pages but quickly reindex them again retaining the rank
• If your site was down longer than that like a week or a month, you might face the problem that my client is facing. Since your website wasn’t available to crawlers for a long period the indexed pages will be completely vanished from the index as well as your rankings. You’ll need to start from the scratch.

Here is a video from Matt Cutts answering a similar question.

Does it affect PageRank?
No, it does not. PageRank depends only on backlinks (which Matt told in that video above) which are certainly not going to be down with your site.