Most project delays are reported in two ways. A red status indicator on a slide, and a revised completion date in the schedule.
Neither of those tells you what the delay is economically worth. They tell you a project is late. They do not tell you what being late is costing the business.
The usual name for that question is cost of delay. The concept that answers it most precisely is drag cost. It is one of the most useful ideas in modern project economics, and it is one of the foundations of how a Value Management Office speaks about delivery in language executives can actually act on.
Where the concept comes from
Drag cost was developed by Stephen Devaux over more than three decades of work on managing projects as investments. His books - Total Project Control and Managing Projects as Investments - laid out the framework. Devaux's thinking is increasingly aligned with where PMI and the wider profession are moving: away from measuring project completion alone, and toward measuring value delivery.
Most of the project management profession was slow to listen. The ideas are now starting to land, in part because the cost of not using them has become harder to ignore.
What is drag cost, and how is it different from cost of delay?
Drag cost is the financial value of the time being added to a project by a specific activity on the critical path.
Cost of delay is the practice of pricing a project's lateness in money instead of a status color, but it only totals what the whole project's delay is worth. Drag cost, developed by Stephen Devaux, narrows that figure to one activity on the critical path at a time, showing which piece of work is actually responsible for the delay.
To get there, two things have to be true. First, the project has a calculable economic value - revenue, savings, strategic benefit. Second, the activity in question is on the critical path - which means accelerating it would bring the project finish date forward.
If those two conditions hold, the maths is straightforward. If finishing the project one week earlier is worth, say, $100,000 to the business, then every week of time that a critical-path activity is adding to the schedule is worth that much in delayed value. That number is the activity's drag cost.
Activities not currently on the critical path normally have a drag cost of zero, because accelerating them will not bring the project finish date forward. They may still matter for other reasons, but they are not currently delaying value realisation.
Cost of delay is the term most people already reach for here, and it gets something right: it prices lateness in money instead of a status color. Where it runs out of precision is that it totals what an entire project's delay is worth, without saying which activity is actually responsible for the days being lost. Drag cost answers that second question. It takes the same idea and applies it to one activity on the critical path at a time, so the organization knows exactly where to spend to get the time back.
The important point is that drag cost does not just price the project delay. It helps identify which activity is economically responsible for that delay.
Why this is different from float, slack, or red status
Drag cost is often confused with concepts the project management profession already has. It is worth being clear about the differences.
- Float and slack tell you how much an activity can slip without delaying the project. Drag cost tells you how much an activity is currently adding to the end of the project. They measure opposite things.
- Red status tells you a project is late. Drag cost tells you what the lateness is worth in money. Status is qualitative. Drag cost is financial.
- Earned value tells you whether work is being completed on schedule and on budget. It does not tell you whether the activity in question is the one limiting when value is realized. Drag cost does.
These distinctions are not academic. They change which activities get the organization's best people, which decisions get escalated, and which conversations happen at executive level.
| Metric | What it tells you |
|---|---|
| Float or slack | How much an activity can slip without delaying the project |
| Status color | Whether a project is late, not what the lateness is worth |
| Earned value | Whether work is on schedule and budget, not which activity is limiting value |
| Drag cost | How much money a specific activity is currently adding to the delay |
What drag cost changes in practice
A function that calculates drag cost across its portfolio gets to ask very different questions from one that does not.
Resource allocation stops being a discussion about who is available and becomes a discussion about where every hour of effort would create the most economic value. The activities with the highest drag cost get the best people, because accelerating them produces the largest financial return.
Delay reporting changes shape. A traditional PMO reports that project A has slipped by 3 weeks. A function using drag cost reports that those 3 weeks are worth $300,000 in deferred revenue, and explains what interventions would recover the time and what they would cost. The conversation moves from operational status to economic decision.
Investment in acceleration becomes defensible. Spending extra money to compress an activity sounds like a budget conversation until you can show the drag cost it is removing. A $50,000 investment to remove $300,000 of drag cost is no longer a budget conversation, it is a return-on-investment conversation, and finance functions know how to have that one.
Why most organizations do not calculate it
If drag cost is this useful, the obvious question is why almost no organizations are using it.
Three reasons:
- It requires every project to have an economic value attached. Many organizations approve projects on a business case and then forget the value side once delivery starts. Drag cost makes that omission visible.
- It requires the critical path to be live and accurate. Most schedules are produced once, signed off, and not maintained with the discipline drag cost requires.
- It changes who gets to influence resource allocation. Drag cost gives the function calculating it a defensible economic argument, which can be politically uncomfortable in organizations where resource decisions are currently made by seniority.
None of these reasons are technical. They are organizational. The maths is straightforward. The harder work is building the operating discipline that lets the calculation happen.
Where this lives in a Value Management Office
Drag cost is one of the metrics that gives a VMO its economic teeth. It is what allows the function to speak about delivery in dollars and dollars rather than RAG ratings, and it is what makes the case for targeted acceleration investment defensible.
It is not the only metric a VMO needs - the investment health of each project also matters, and that is what Devaux's DIPP metric is built for. But drag cost is the one that most directly connects what is happening inside a project to what it is costing the organization. Without it, delay is a status indicator. With it, delay becomes an economic number the business can act on.
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