Elastic systems, either synchronous or asynchronous, can be optimized for the average-case performance when they have units with early evaluation or variable latency. The performance evaluation of such systems using analytical methods is a complex problem and may become a bottleneck when an extensive exploration of different architectural configurations must be done. This paper proposes an analytical method for performance evaluation using symbolic expressions. Two version of the method are presented: an exact method that has high run time complexity and an efficient approximate method that computes the lower bound of the system throughput.