The base date of cost data, or base date, is the date at which the costs in a cost estimate or cost plan apply, excluding any adjustment for risk allowances or inflation.
Every estimate needs a stated base date so that readers know what price level it reflects. Under NRM 1, allowances for inflation are calculated forward from the base date: tender inflation runs from the base date to the date of tender return, and construction inflation runs from the date of tender return to the mid point of the construction period. When historical cost data from earlier projects is used for benchmarking, it is first adjusted to the base date of the new estimate using a suitable cost or tender price index.
- State the base date clearly on every estimate and cost plan.
- Update it when the estimate is repriced, rather than leaving an old date in place.
Related terms: tender inflation, construction inflation, cost index, cost plan.
