The proper setting of support ventilation aims to follow the patients' demands, ensuring adequate assistance to their respiratory effort. Effort assessment is thus necessary. But invasive procedures like measuring transdiaphragmatic pressure (Pdi) are impractical in long-term ventilation. Our purpose was therefore the development of the Occlusion+Delta (O+D) method for non-invasive continuous assessment of effort, quantified by the inspiratory pressure-time-product (PTPinsp), during ventilatory support. Flow and airway pressure were measured from 25 healthy volunteers at three effort levels. For the non-invasive method, short expiratory occlusions were executed each three to seven cycles to estimate resistance and compliance with a fitting algorithm fed with the differences between occluded and undisturbed cycles. Signals and estimates were then used to calculate the effort. For the validation of O+D, its estimations were compared to the results from invasive measurement of Pdi using balloon catheters. The agreement between PTPinsp from the invasive measurement and the proposed alternative was confirmed by regression analysis (PTPO+D=1.13PTPPdi- 0.85, R=0.84) and calculation of their differences (mean±SD=1.78±7.18 cm H2O s). Repeated execution of the non-invasive O+D method facilitates a safe automatic assessment of respiratory mechanics and breathing effort, promoting the rapid recognition of changes in patient's demands and the adaptation of support.