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Extension of time calculator

Work out your EOT notice deadline and entitlement under AS 4000, AS 4902 or AS 2124, including how each form treats concurrent delay and what happens if the superintendent says nothing.

1. Contract form

Clause 34. Notice within 28 days to the Superintendent and the other party.

AS 4000 runs the 28 days from awareness of the cause, not from when the delay ends. For a rolling delay the clock starts on day one.

My contract amends the standard notice period

Amendments are common and they matter. Some government principals substitute 20 business days and expressly label it a time bar. Note that 20 business days is not a shorter deadline than 28 calendar days. It is the same or longer once holidays fall in the window. What changes is that late notice becomes an unambiguous bar rather than an arguable one.

Is late notice fatal? Clause 34.3 is drafted as a condition precedent, but clause 41.2 says a late claim shall “neither bar nor invalidate” it. That conflict is unresolved by Australian appellate authority, and clause 41.2 is very commonly deleted by amendment, which removes the argument entirely. Check whether yours survives.

2. Delay events

Date for Practical Completion (before any EOT)

Event 1

What happened

Cause

Date you became (or should reasonably have become) aware of the causation

Days of delay claimed

On the critical pathConcurrent with a delay you caused

Notice deadline: Mon 28 Sep 2026. 28 days left

0 days claimable, time and delay costs. A compensable cause: time and delay damages under cl 34.9.

Your claim

days claimable

Revised date for Practical Completion: Wed 31 Mar 2027

If granted in full. Every day granted is a day of liquidated damages you are not exposed to.

Silence works for you under this form. If the Superintendent does not give a written direction within 28 days of your claim, clause 34.5 deems an extension of time granted as claimed. Silence works in your favour under this form.

Also required: Clause 34.2 also requires prompt written notice of anything that will probably cause delay, as soon as you become aware of it. That is a separate obligation from the 28-day claim, and it has no fixed period.

Exclusions from qualifying causes sit in Annexure Item 23; additional compensable causes in Item 26. Both are project-specific. Read them.

Concurrent delay: the forms disagree

AS 4000 and AS 4902 apportion. Clause 34.4 requires the Superintendent to split the delay between qualifying and non-qualifying causes according to their contribution.

AS 2124 does the opposite. Where any concurrent cause is not a qualifying cause, you get no extension at all for the concurrent period. A contractor who assumes AS 2124 behaves like AS 4000 can lose the entire claim.

Beyond the contract, the general law on concurrent delay in Australia is genuinely unsettled. The competing approaches are first-in-time, the English but-for approach, and apportionment, and there is very little Australian appellate authority because these disputes almost always go to arbitration. This tool applies your contract's rule and does not attempt to resolve the law. Take advice on anything contentious.

See what those days are worth in liquidated damages →

Every day of extension granted is a day of LDs avoided. The two calculations are the same question from opposite ends.

Indicative only and not legal advice. Entitlement depends on your executed contract, its amendments and the facts. Standard forms are very commonly amended, including to shorten the notice period and to convert it into an express time bar. Whether late notice bars a claim is contested in Australia and turns on the drafting. Concurrent delay is unsettled at general law. Confirm against your contract and take advice before relying on any date or figure here.

The notice period is where claims are lost

Most extension of time claims that fail do not fail on the merits of the delay. They fail because notice was given late, and the contract made timely notice a condition of entitlement.

The difficulty is that the standard forms do not agree on when the clock starts. Under AS 4000 and AS 4902 the period runs from when the contractor becomes aware of the cause and its likely effect on the programme. Under AS 2124 it runs from when the delay occurs.

That difference is not academic. A cause you become aware of before it produces any delay starts the clock at different moments under the two families, and a notice that is comfortably in time under one may be well out of time under the other.

Concurrent delay: apportioned or forfeited

Concurrent delay is where two causes operate at the same time: one entitling the contractor to an extension, one not. How the contract treats it determines whether you get anything at all.

AS 4000 and AS 4902 direct that the extension be apportioned between the causes. AS 2124 does not: where a concurrent cause is one for which the contractor is responsible, entitlement is forfeited.

This is one of the most commercially significant differences between the forms and it is frequently missed at tender, where the amendment schedule gets read for the liquidated damages rate and not for this.

Deemed grants, and the silence that helps you

Under AS 4000 and AS 4902, if the superintendent does not respond to a claim within 28 days, the extension is deemed to have been granted for the period claimed. Silence works in the contractor’s favour.

AS 2124 contains no equivalent. Silence is simply silence, and the claim remains undetermined indefinitely unless somebody pursues it.

Knowing which regime applies changes what you do when a claim goes unanswered. Under one, the correct action may be to record the deemed grant and proceed. Under the other, it is to keep pressing.

Amendments matter more than the base form

Almost no Australian contract uses a standard form unamended, and EOT clauses are among the most heavily amended. Notice periods get shortened, deemed grants get deleted, and time bars get tightened.

One common amendment replaces a 28 calendar day notice period with 20 business days. It is worth being precise about what that does: 20 business days is the same as 28 calendar days when no public holidays fall in the window, and longer when they do. The material change is not that the period is shorter. It is that the amendment usually converts the requirement into an unambiguous bar on entitlement.

Read the amendment schedule, not the standard form. The calculator lets you override the periods for exactly this reason, and the override is the normal case rather than the exception.

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