Time-to-first-byte (TTFB) is one of the most useful website performance metrics. It’s also one of the hardest to improve. Caching plugins can’t do much for it; actually they contribute to it. Caching plugins don’t fix cache warm-up, authenticated sessions, submissions / processing, and administration. To improve those you need to get TTFB in range. The recommended target is 0.5 seconds. Here’s my tips to optimize your TTFB.