What is a Class D estimate? It is the first, order-of-magnitude cost estimate for a building project, prepared from a functional program and broad concept, and it is generally accurate to about ±20 to 30%, according to Canada’s Guide to Cost Predictability in Construction. Alberta’s 2026 framework uses a wider, lopsided range for the same stage: 30% below to 50% above the estimate.
Below: Class D estimate accuracy, how it compares with Classes C, B and A, what contingency it should carry, and when to use it. For the full walk-through of all four classes, see our estimate classes guide.
Class D estimate accuracy
A Class D estimate is built before there are drawings to measure. The estimator works from the functional program (the rooms, areas and services the building must provide), an elemental summary and a rough cost per square metre. That’s why its accuracy band is so wide.
View the data
| Class | Low complexity | High complexity | Design stage |
|---|---|---|---|
| Class D | ±20% | ±30% | Functional program, concept |
| Class C | ±15% | ±20% | Schematic design |
| Class B | ±10% | ±15% | Design development, working drawings |
| Class A | ±5% | ±10% | 100% construction documents |
The federal guide sets the band by project complexity and type: simple new buildings sit near ±20%, while complex projects and renovations sit near ±30%. Unique projects or unusual risks can widen it further.
Estimate classes A, B, C and D compared
Each class matches a design stage. The more design information exists, the narrower the range:
- Class D: functional program and broad concept. Used for feasibility, options and the first budget request.
- Class C: schematic design, generally up to about a third complete. Used to confirm the budget and the scope.
- Class B: design development and working drawings, updated as drawings advance. Used for cost control during design.
- Class A: complete construction documents, just before tender. Used to check the bids.
Alberta’s framework, which maps the Canadian classes to the ASTM classes, makes one point the symmetric ± ranges hide: early estimates are far more likely to come in high than low.
View the data
| Stage | CIQS class | Low | High |
|---|---|---|---|
| Functional | Class D | -30% | +50% |
| Schematic design | Class C | -20% | +30% |
| Design development | Class B | -15% | +20% |
| 50–75% construction drawings | Class B | -10% | +15% |
| 95–100% pre-tender | Class A | -5% | +10% |
What a Class D number really means
The simplest way to see the risk is to apply the ranges to a single number. A $10 million Class D estimate is not a $10 million project. It is a project that will most likely land somewhere between $7 million and $13 to $15 million.
| Basis | Range | Final cost |
|---|---|---|
| Federal, low complexity | ±20% | $8M–$12M |
| Federal, high complexity | ±30% | $7M–$13M |
| Alberta, functional stage | −30% / +50% | $7M–$15M |
That doesn’t make the Class D estimate wrong. It makes it early. The mistake is treating it as a fixed budget, announcing it publicly or locking funding to it before the design has caught up.
How much contingency should a Class D estimate carry?
There’s no single correct percentage, and Canadian public guidance deliberately avoids one. The federal guide says a Class D estimate should carry design, pricing, bid, construction, escalation and scope contingencies, plus allowances for unknown items and inflation in the unit rates. Alberta’s 2026 framework goes further: contingency must come from a risk analysis, blanket percentages need clear justification, and the design and pricing contingency should fall to zero by the Class A or contract award stage.
In practice, that means two things for owners. First, ask your cost consultant to show each contingency separately, not as one lump. Second, expect the design and pricing contingency to shrink with each class while construction contingency remains. Our posts on how much contingency to carry and escalation allowances cover the numbers side.
When to use a Class D estimate
- Feasibility and business cases. Comparing options and deciding whether a project is worth pursuing.
- The first funding request. Presented as a range, with the class stated on the cover.
- Not for fixing a contract price. No contractor price should be benchmarked against a Class D number.
- Not for public announcements. If the number must be announced, announce the range.
For a quick sense check of your Class D number, compare it with our GTA cost benchmarks, and tie each estimate update to a decision point in your stage-gate process.
FAQ
What is a Class D estimate?
A Class D estimate is the first, order-of-magnitude cost estimate for a building project. It is prepared from an initial functional program and broad concept, usually as an elemental summary using cost per square metre.
How accurate is a Class D estimate?
Canada's Guide to Cost Predictability in Construction puts Class D accuracy at about plus or minus 20 to 30%, depending on complexity. Alberta Infrastructure's 2026 framework uses minus 30% to plus 50% for the functional stage.
What is the difference between a Class A and a Class D cost estimate?
A Class D estimate comes at the start, from a functional program, and is accurate to about plus or minus 20 to 30%. A Class A estimate comes at the end of design, from complete construction documents, and is accurate to about plus or minus 5 to 10%.
What are estimate classes A, B, C and D?
They are the four Canadian classes of construction cost estimate, from least to most design information: Class D (functional program), Class C (schematic design), Class B (design development and working drawings) and Class A (complete construction documents, pre-tender).
How much contingency should a Class D estimate carry?
Canadian public guidance doesn't set one percentage. The federal guide says a Class D estimate should carry design, pricing, bid, construction, escalation and scope contingencies, and Alberta requires contingency to be set from a risk analysis rather than a blanket percentage.
The bottom line
A Class D estimate is a range of about ±20 to 30%, and possibly 50% on the high side, dressed up as a single number. Use it to decide whether to proceed, not to fix the budget. Then narrow it, class by class, as the design develops.
Need an independent check on an early estimate? Try our owner tools, or book a 30-minute call.
Sources: Joint Federal Government/Industry Cost Predictability Taskforce, Guide to Cost Predictability in Construction (2012), Canadian Construction Association; Alberta Infrastructure, Project Cost Framework for Alberta Infrastructure Projects (May 1, 2026); Alberta Infrastructure, Classes of Construction Cost Estimates, Design & Technology Series #19 (2025). This article is general information, not financial advice.