In-plane macrocrack initiation of as-deposited, thermally aged, and in-service used thermal barrier coatings (TBCs) with different levels of pores and microcracks, affecting the Young’s modulus (Ec), have been studied using a newly developed protruded TBC bending technique in conjunction with a finite-element stress analysis. In-plane macrocracking along splat boundaries initiates from a curved edge of protruded TBC under the out-of-plane and shear applied and residual stresses resolved from the in-plane components. The TBC macrocracking is characterized by the critical strain energy density [(σ*e)2/Ec], which represents the material propensity, i.e., the ratio of the interfacial cohesive energy to the critical microcrack size (γf/ac), and the residual stress effect. The cracking behavior strongly depends on the type of TBC, subjected to different thermal history, and the substrate machining. Ungrooved substrate specimen tests indicate that while the as-deposited TBC has through-thickness fluctuation in (σ*e)2/Ec, the aged and used TBC exhibits a trough and peak of (σ*e)2/Ec near the middle section, respectively. In grooved or thinner substrate specimens of the TBCs where the residual stress is partially relieved, cracking further away from the interface occurs at lower and constant (σ*e)2/Ec representing γf/ac. It is interpreted that the through-thickness variations of (σ*e)2/Ec in the ungrooved substrate specimen of the various TBCs are more largely affected by the out-of-plane compressive residual stress than γf/ac.