Additive manufacturing systems (AMS) are disclosed. The AMS may include a movable build platform, and a calibration system operably connected to the build platform. The calibration system may include a reflective element operably coupled to the build platform, a first calibration model positioned above and vertically offset from the reflective element, and a first camera substantially aligned with the first calibration model. The first camera may be visually aligned with the reflective element to capture a first reflective image of the first calibration model as reflected by the reflective element. The calibration system may also include at least one computing device operably connected to the build platform and the first camera, and configured to calibrate the build platform by: adjusting an actual inclination of the build platform in response to determining the first reflective image differs from a predetermined image of the first calibration model.