Most WordPress speed depends on the MySQL database, which means your database:

1. Should be isolated from other bloggers. With most hosting companies you are sharing a database with other bloggers to some degree. The problem is when you don’t have reserved, priority access. If the server is stressed to the max to increase profits for the host, your readers/visitors are forced to wait for an open connection to the database. This is the #1 root cause of slow blogs.
2. Your whole database should fit in RAM. Cheaper hosts won’t do this. Random Access Memory is really fast. Also WordPress needs extra memory to maximize its multitasking capabilities. Think of a checkout line at the store with people waiting. More RAM buys you more cashiers to serve everyone in line faster. (Assuming the server is otherwise optimally configured.)
3. Your database “engine” should be InnoDB. With very old WordPress blogs, you might need your engine upgraded from MyISAM.

Or it could be a DNS issue. Some hosts take up to 7 seconds just for the DNS lookup! Most blog hosts/registrars are not DNS specialists. If you want the best performance, you should check your DNS performance & consider the value of a DNS upgrade.

Or it could be a PHP issue. I’m a PHP developer since 2001. (Before that I was a Perl/Java guy.) Sometimes plugins are poorly designed, or were not designed for your specific needs. Whatever the problem is, I can fix it.

If we’re not already connected, get in touch with me.