NEC Option X1 Start date for fluctuation calculation

We have are in an NEC contract option A with X1 fluctuations.The base date for fluctuations was October 20, the contract commencement date was Jan 21 and start on site was March 21. X1 says fluctuations will be calculated quarterly but does not give the date when the first calculation should be done. When should the first calculation be done.

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If this is the ECC form then a calculation is made each time the amount due is assessed. It looks like your contract has been amended to a quarterly assessment but without providing details of when this is actually done (quarterly from the starting date / calendar year etc). I would notify an ambiguity and request clarity of when this should commence.


To my understanding, Base date is commonly the date when Contractor determine the percentage of labour as well as materials usage using the certain period of figure for the Project on the tender stage. To your case, is it Oct, 20?

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