Worst-case execution time (WCET) is the longest time it takes a computer program to finish running. It measures how long it takes a computer to complete all of the instructions it needs to do in order to finish the program. For example, if a program has 10 instructions, the WCET shows how long it would take the computer to complete all 10 instructions, no matter what order they are in and no matter what other tasks the computer is running at the same time.