An EOT (Extension of Time) claim is one of the most contested aspects of EPC contract management. Under FIDIC and most bespoke contracts, an EOT that is late-noticed, poorly analysed, or thinly evidenced gets rejected — even when the underlying delay was real. This guide covers the three delay-analysis methods planners use and when each is appropriate.
The three-part test every EOT must satisfy
Before selecting a delay-analysis method, be clear about what you are proving:
- Entitlement. Does the contract entitle you to EOT for this type of event? (Force majeure, employer instruction, employer default, unforeseen ground conditions, etc.) Verify the clause number.
- Causation. Did this event actually delay the critical path? Or was there parallel float that absorbed it?
- Quantum. How many days of EOT should be awarded? This is where the analysis method matters.
A perfectly-analysed claim with weak entitlement is dead. A perfectly-entitled claim with no causation proof is dead. All three must be satisfied.
Method 1 — Time Impact Analysis (TIA)
The prospective method. Preferred by most contract administrators because it is contemporaneous.
How it works: Take the schedule as it stood immediately before the delay event. Insert the delay event as a new activity. Reschedule. The difference between the original completion date and the new completion date is the EOT.
When to use: When you have a clean pre-event baseline schedule and the delay event is well-defined (e.g. an instruction with a clear date). This is the FIDIC-preferred method for prospective claims.
Weakness: If the schedule quality is poor, TIA produces garbage results. Requires a rigorous baseline discipline throughout the project.
Method 2 — Windows Analysis
The retrospective method. Preferred when multiple delay events overlap.
How it works: Divide the project into time windows (typically monthly or by major milestone). For each window, compare the schedule at the start vs the schedule at the end. Attribute the delta to the delay events that occurred in that window.
When to use: When you have many small delay events that compounded, when the project has finished, or when the client requires retrospective validation.
Weakness: More labour-intensive than TIA. Requires monthly saved baselines (P6 baseline management discipline).
Method 3 — Collapsed As-Built
The reverse method. The as-built schedule with delay events removed shows what the completion would have been without them.
How it works: Start with the actual as-built schedule at project end. Delete or shorten the activities affected by the delay event. Reschedule. The difference between actual completion and the collapsed completion is the EOT.
When to use: When TIA is impossible because there is no clean pre-event schedule, or when Windows is impossible because monthly baselines were not saved. This is the fallback method.
Weakness: The most contested method. Client teams often reject collapsed-as-built results because they involve significant judgement about what activities would have looked like without the delay.
Documentation the claim depends on
The best analysis in the world fails without underlying evidence. Every planner working on EOT-prone contracts should maintain:
- Signed baseline schedule with date-stamped client approval
- Monthly updated schedules saved as separate P6 baselines
- Daily site diary entries linked to schedule activities
- Correspondence log (RFIs, site instructions, employer instructions)
- Weather records for weather-related claims
- Photographs date-stamped and linked to activities
- Meeting minutes documenting instructions and decisions
The 28-day notice trap
Under FIDIC 1999 Clause 20.1, the contractor must give notice of an EOT claim within 28 days of becoming aware (or when they should have become aware) of the delay event. Miss this window and you may lose entitlement entirely — even for a valid claim.
FIDIC 2017 introduced Clause 20.2.1 which is even stricter. Read your specific contract carefully.
Where planners typically add or lose value
Add value:
- Rigorous baseline discipline throughout the project (BL0, BL1, monthly BLs)
- Contemporaneous delay documentation, not retrospective reconstruction
- Working closely with the contracts team on notice timing
Lose value:
- Weak WBS design that makes attribution impossible
- Missing baselines when needed for Windows analysis
- Poor progress-updating discipline (activities marked complete before actually complete)
EOT analysis is one of the highest-value skills a planner can have. Very few Primavera courses teach it seriously — ours does. See the Primavera P6 curriculum for the delay-analysis modules.