Uptime, in payments technology, is the proportion of time during which a system such as a payment gateway, processor, card network or bank interface is working and able to handle transactions. It is stated as a percentage. An uptime of 99.9 percent allows about 8.8 hours of downtime in a year, and 99.99 percent allows about 53 minutes.
Providers commit to a figure in a service level agreement, usually with service credits if it is missed. The headline number needs careful reading. Agreements often exclude planned maintenance, measure only whether the system responds and not whether payments succeed, and average across all customers. A service can be technically up while approving few transactions or responding slowly, so merchants also watch authorization rate and latency. Because every outage means lost sales, larger merchants protect themselves with failover routing to a second provider.