This report analyses two serious incidents involving an insufficient thrust setting for take-off that occurred with the same operator. Besides the insufficient thrust setting, the calculated take-off speeds were invalid. In both incidents the required safety margins for take-off performance were not met, increasing the risk of a runway overrun, tail strike and a collision with an obstacle after departure. During the first serious incident (2014) the operator made use of manual performance calculations, whilst the second serious incident (2015) occurred after the operator had introduced digital performance calculations on an Electronic Flight Bag (EFB). These incidents are not unique. Worldwide, numerous incidents with erroneous take-off parameters occurred over the years.