The input vector-oriented reliability estimation of sequential circuits plays an important role in predicting their reliability boundaries and identifying their reliability-critical gates. This article presents an input vector-oriented programmable method based on fanout-source tracking and reduction for the reliability evaluation of sequential circuits. In the proposed method, fanout-source tracking is introduced to track fanout sources of a computing node to determine the fanout sources affecting the node output signals. An iterative reduction method is presented to eliminate duplicate calculations caused by fanout reconvergences without reducing the accuracy. A dynamic fanout relevance-keeping-based calculation method is used to approximate the trend probability vector of low-priority nodes outputting “0” and “1” to accelerate the calculations at a small accuracy loss. A complexity-accuracy tradeoff method based on a programmable fanout source length is designed to facilitate reasonable calculations as needed. Experimental results on large-scale circuits show that the average relative error of the proposed method is 1.01% with Monte Carlo (MC) as a reference. Moreover, the proposed method is 4,308.13 times faster than the MC on average, but its average memory cost is 3.40 higher than that of the MC model. Compared with similar methods, the proposed method not only is suitable for large-scale circuits and performs better in accuracy, but also enables programmable computation to dynamically balance the tradeoff between accuracy and speed as actual needed, resulting in better applicability and scalability.