This is a substantial hike from its previous estimate of R650m.
McKinsey worked alongside Gupta-linked Regiments Capital at Transnet.
The US consulting giant McKinsey & Co has agreed to pay back R870 million for consulting work it did at Transnet alongside the Gupta-controlled Regiments Capital.
The amount announced by McKinsey and Transnet in a joint statement on Tuesday is much larger than the R650 million put forward last year.
In December, the Zondo commission into state capture announced that the US company has agreed to pay back R650 million to Transnet and SAA for work it did on consulting contracts.