Source: https://www.quantsurv.com/delay-and-disruption/faq/how-is-an-extension-of-time-calculated
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Content reviewed: 2026-09-30

# How is an extension of time calculated?

An extension of time assesses the effect of qualifying events on the contractual completion date. It is not simply the number of days an activity stopped.

By [Jack Butler-Kettle](<https://www.quantsurv.com/about#who-we-are>) · Updated 30 September 2026

Guidance for England and Wales. Check the contract, amendments and facts that apply to your job.

## The answer

Identify the applicable event and notice requirements, then assemble the programme and progress records. The [SCL Delay and Disruption Protocol](<https://www.scl.org.uk/sites/default/files/documents/SCL_Delay_Protocol_2nd_Edition_Final.pdf>) discusses delay analysis; it is guidance, not the contract. The method must suit the terms, available records and timing of the assessment.

Explain the affected activities, their sequence and their effect on completion. Test available float, mitigation and other causes rather than adding every delay together. [Concurrent delay](<https://www.quantsurv.com/delay-and-disruption/faq/concurrent-delay>) needs particular care.

A simple calendar illustrates an assumed result; it cannot determine entitlement. [Extension of Time Support](<https://www.quantsurv.com/delay-and-disruption/services/extension-of-time-support>) organises the notices and event records alongside the client's appointed planner. Separate [time entitlement from loss and expense](<https://www.quantsurv.com/delay-and-disruption/faq/relevant-events-and-relevant-matters>).

## Example

### The facts

A fictional subcontract has a completion date of 10 June. Access to an activity is withheld for ten calendar days.

### What happens

1.  The planner checks the applicable programme, progress and sequence. The assumed analysis finds that four of those days did not affect completion.
    
2.  For this illustration, the remaining six days are accepted as qualifying completion delay, with no competing delay or other adjustment.
    
3.  The accepted six-day extension moves completion to 16 June. The calculation does not establish any entitlement to six days of additional cost.
    

### What this shows

Ten days of interrupted activity produce six days of extension only under the stated assumptions. Another programme or contractual allocation can produce a different result.

## Sources

1.  [Delay and Disruption Protocol, 2nd edition, February 2017](<https://www.scl.org.uk/sites/default/files/documents/SCL_Delay_Protocol_2nd_Edition_Final.pdf>). Society of Construction Law.

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