Short answer
To prove a project is late you need three things: the baseline schedule the developer committed to, an independent dated measurement of what was actually built, and a method that converts the gap into time. Earned schedule does the last step: it finds the date by which the plan expected today's progress, and the difference from today is the delay.
What counts as proof that a project is late?
A claim that a building is late is only as strong as its weakest link. You need the baseline (the approved schedule or the contractual milestone dates), a measurement of actual progress that the developer did not produce, and a transparent calculation. Remove any of the three and the argument collapses into opinion.
- The baseline: signed programme, loan disbursement schedule or permit conditions
- The measurement: dated, independent, repeatable, with original images kept
- The method: a calculation anyone can reproduce from the same inputs
Why is percent complete not enough?
'Tower B is 47% complete' says nothing on its own about lateness. It only becomes meaningful next to what was planned for today. And even '47% earned vs 61% planned' is a gap in work, not in time, and it cannot be put straight into a delay notice. Classic earned-value schedule variance is also expressed in money and tends towards zero as a project ends, even when it finishes months late.
How does earned schedule turn progress into days?
Take the planned progress curve from the baseline. Find the date on that curve where planned progress equals the progress actually earned today. That date is the earned schedule (ES). Compare it with the actual time (AT), today's date.
- Schedule variance in time: SV(t) = ES − AT (negative means late)
- Schedule performance index: SPI(t) = ES ÷ AT (below 1.0 means late)
- Independent estimate of completion: planned duration ÷ SPI(t)
What does a worked example look like?
Take a product example. Tower B's baseline planned 61% of structure and envelope by 7 September. A drone flight on 7 September measures 47% earned. On the baseline curve, 47% was scheduled for 10 August. So ES = 10 August, AT = 7 September, and SV(t) = −28 days: the tower is 28 days behind the plan it was financed on.
| Input | Value | Source |
|---|---|---|
| Planned progress today | 61% | Baseline programme, p. 4 |
| Earned progress today | 47% | Drone flight, 7 Sep, 3D model |
| Date plan reached 47% | 10 Aug | Baseline curve |
| SV(t) | −28 days | ES − AT |
How do you make the measurement independent and tamper-evident?
Fly on a fixed cadence with a saved route, keep every original image, and record a cryptographic hash (such as SHA-256) of each file at upload. The hash lets anyone confirm later that the image in the report is the image that was captured. Record capture time and position from the drone's metadata, and annex the schedule pages the milestones came from. control.io does all of this by default.
How should the delay be reported?
Report per floor and per trade, not only for the whole building: 'Floor 13 structure, 34 days late' is actionable, '12% behind' is not. Show the image that proves each finding next to the milestone it tests and cite the page of the schedule. Keep the tone factual; the report's job is to establish the facts, and decisions about notices, penalties or tranche holds belong to the reader and their advisers.
Sources
- Lipke, W. (2003). 'Schedule is Different'. The Measurable News. Original description of the earned schedule method.
- McKinsey Global Institute / McKinsey & Company (2015). 'Imagining construction's digital future'. Reports that large projects typically take 20% longer to finish than scheduled.
About the author
control.io Field Engineering Team
Civil engineers, licensed drone pilots and photogrammetry specialists who run control.io's site supervision and inspection flights.