Worst Case Execution Time (WCET) estimation is substantial for scheduling analysis of real-time systems. Estimating WCET encompasses performing program analysis as well as modeling the impact of complex micro-architectural features of modern processors. In this paper, we present a novel method to estimate the WCET using a Domain Specific Language (DSL) taking dynamic branch prediction into account. We illustrate how to extend the Constraint Generation Language (CGL), a DSL designed to describe highlevel constraints, to automate the constraints generation from a program’s branch flow graph and control flow graph. The validity of our technique is shown by tight and safe estimates acquired on realistic benchmarks.