Latency is the time delay between sending a request and receiving the first response, usually measured in milliseconds. Proxies add latency because traffic makes an extra hop through the proxy server before reaching its destination, and the physical distance and quality of that proxy server directly affect how much delay is added.

Datacenter proxies generally have the lowest latency, since they run on dedicated, well-connected server infrastructure; residential and mobile proxies typically add more, because the request is routed through a real consumer connection with less predictable performance. For latency-sensitive tasks, like real-time price checks against fast-changing data, proxy latency can matter as much as raw bandwidth.

Latency is typically dominated by physical distance and the number of network hops a request travels through, which is why a proxy located far from either the client or the target server tends to add noticeably more delay than one positioned closer to the path a direct connection would take.