When does interest start?
Interest commences on the day the money was due to be paid (1).
When does interest end?
Interest ceases on the day the money is paid.(2).
GST
You do not claim 67P interest with respect to the GST component of a progress claim.(3)
When you claim for the interest you also claim for the GST payable on the interest.
Citations
(1) Civil Mining & Construction Pty Ltd v Wiggins Island Coal Export Terminal Pty Ltd (No 3) [2018] QSC 60 (26 March 2018) paragraph 164
(2) ibid. paragraph 164
(3) ibid. paragraph 113