Base date in construction contracts
A 'base date' is a reference date from which changes in conditions can be assessed.
The base date in construction contracts is generally used as a mechanism for the allocation of risk between the client and contractor for changes that might occur in the period between the contractor pricing the tender and the signing of the contract. This period can be very long and changes that occur may have a significant impact on the costs of the works.
The base date sets the reference date from which the conditions under which the tender was prepared are considered to have been known by the contractor and so are properly reflected in their price. If specified conditions change before the contract is implemented, then the contract may be adjusted to reflect this.
On very small projects, where the time frame is short, this may not be considered necessary. On larger projects, the base date can be used to allow changes to the contract sum, or sometimes extensions of time, or even to determine which rules will apply to the contract (for example which edition of arbitration rules).
The exact provisions will depend on the specific form of contract that is adopted. For example, in the Joint Contracts Tribunal (JCT) Design and Build Contract, the base date determines the allocation of risk in relation to changes in statutory regulations, changes to VAT exemptions and changes to definitions of dayworks.
Traditionally the base date was set as the date of tender, however this was sometimes found to give rise to uncertainty because of the complexity and duration of tendering procedures. The usual practice now is to insert a date in the contract linked to the date of the return of tenders. The FIDIC suite of standard conditions of contract (the Red Book and Yellow Book), set the base date at 28 days before the latest date for the submission of tender. The JCT Design and Build Contract suggests a date that is 10 days prior to the date of the return of tenders.
NB Fluctuation clauses are a way of dealing with inflation on large projects that may last for several years. The contractor may be asked to tender based on current prices and then the contract makes provisions for them to be reimbursed for price changes over the duration of the project (a fluctuating price). This may be done by setting a base date for specified items and defining the price indices by which fluctuations will be assessed. Fluctuation may allow for; changes in taxation; changes in the cost of labour, transport and materials; and even changes in head office or administrative costs.
 Find out more
 Related articles on Designing Buildings Wiki
- Completion date.
- Contract conditions.
- Contract sum.
- Extension of time.
- Liquidated and ascertained damages.
- Loss and expense.
 External references
Featured articles and news
Rebekah Paczek takes a look at the party conferences and by elections and considers what it all means for planning and development.
In a separate article, Rebekah highlights the key recommendations of the Lyons Housing Review, an independent review carried out by Sir Michael Lyons for the Labour Party’s Policy Review.
First Welsh Planning Bill introduced to create a streamlined planning system supporting the delivery of the homes, jobs and infrastructure in Wales.
Defining the level of development that BIM elements should achieve at different stages of a project.
We've published a step-by-step project plan for anyone trying to create their own self-build dream home. It gives detailed guidance from the moment self building becomes a possibility through to walking into the completed home.