Superelastic NiTi exhibit recoverable strains of several percent stemming from reversible martensitic transformation. Besides medical devices relying on superelasticity, the accompanying latent heat exchange is being considered for solid state cooling. Both application fields require fatigue properties of industrial standards that are, however, not met for these alloys. In fact, plastic deformation processes coupled with martensitic transformation lead to premature fatigue failures. For any particular NiTi alloy condition, multiple isothermal deformation experiments are usually performed to identify a save operating stress-temperature window, where the activation of irreversible processes is limited. Instead of this approach, we implemented a deformation infrared calorimetry and tensile tests in temperature gradient that enabled to measure temperature resolved stress–strain responses, deformation work and released heat during a single tensile tests. In particular, the infrared calorimetry coupled with a thermodynamic model enabled to evaluate the amount of martensite volume fraction transforming at the shear-band front propagating in the sample subjected to tension. Using these in-situ methods and post-mortem diffraction techniques, we analyzed temperature and microstructure dependent tensile behavior of initially cold-worked superelastic NiTi wires of 1.78 mm with microstructures adjusted to range from recovered up to fully recrystallized. In summery, non-monotonous temperature dependencies of overall ductility and with martensitic transformation associated strains and volume fractions were identified. The save temperature window decreased down to room temperature for the recrystallized condition. Surprisingly, the regime of largest transformation strains and ductility was correlated with incomplete martensitic transformation and appearance of austenite deformation twin bands rationalized as relicts of martensite deformation twinning.