This paper discusses new findings on fatigue crack growth in an NiTi shape memory alloy. Despite the importance of the topic, there are very few papers that systematically studied fatigue crack growth with investigation of measurements of effective stress intensity at crack tips. It has become clear that one must account for the crack tip wake closure forces in modeling of crack tip stress intensity as they could produce net forces that are substantial. The tractions in the crack wake can reduce the driving forces but the calculation is rather complicated. Instead, we present stress intensity determination based on experimental displacement measurements at crack tips. We utilize digital image correlation to establish vertical and horizontal displacements in NiTi. We then compare the stress intensity determination based on regression of displacement results, which is termed the effective stress intensity range, with that of the stress intensity range based on LEFM. We find that the effective stress intensity range is lower than that based on classical LEFM solution, the difference being more significant at longer crack lengths.