The predictability of the computation time of program modules is very important for estimating an accurate worst-case execution time (WCET) of a task in real-time systems. Dynamic storage allocation (DSA) is a common programming technique. Although many DSA algorithms have been developed, they focus on the average execution time rather than the WCET, making it is very difficult to calculate their WCET accurately. In this paper, we propose a new algorithm called Half-Fit whose WCET can be calculated accurately. The algorithm finds a free block without searching on a free list or tree, allowing extra unusable memory called incomplete memory use. In a simulation following a queueing model of M/G//spl infin/, Half-Fit has the advantage over the binary buddy system of more efficient storage utilization. The binary buddy system is a conventional algorithm whose WCET can be calculated.