A scalable method that simulates the propagation of Single Event Transients (SET) and Single Event Upsets (SEU) for test set sequences is presented. Soft Error Rates (SER) of flip-flops are computed considering SET and SEU propagation. A novel critical path tracing-based approach is proposed to propagate fast and accurately SET and SEU through the time frames of the test sequence considering all applicable masking effects. Experimental evaluation on the larger ISCAS’89 and ITC’99 benchmarks shows that effective SERs calculated using the proposed method are very close to those by exact fault simulation, and it is considerably less than methods that calculate SER by applying the patterns independently. SER accuracy is ensured by the very low pessimism and low optimism in SET and SEU propagation.