Construction Contingency: How Much to Carry at Every Project Phase

A construction contingency percentage has no single correct value. AIA cites design contingency of 5-10% of construction cost and design-build contractor contingency of 5-10%, while Colorado state GMP rules use about 3-3.5% construction contingency plus 2.5% bidding contingency. Early-design budgets carry more, and renovations carry more still.

This is one chapter of our construction cost estimating guide, which shows where contingency sits in the full estimating process.

What is construction contingency?

Contingency is money set aside for costs that cannot yet be identified. It is not a pad on a good estimate and not a slush fund for owner wishes. It exists because every estimate carries uncertainty, and the less complete the design, the more of it there is. The types of construction estimates article shows how accuracy ranges narrow from about 25% at concept to about 10% at construction documents.

Contingency is also not escalation, which allows for price change over time, and not an allowance, which holds a place for a known item that has not been priced. Keep all three on separate lines.

What are the three types of contingency?

AIA's guidance distinguishes three, and the difference is who controls the money.

Treating them as one pool is the usual cause of confusion. A design reserve should shrink to zero by the time drawings are complete, because the risk it covers disappears. The owner's reserve must survive through construction, because unknown conditions and scope changes appear then.

How much design contingency should you carry?

AIA says design contingency is usually 5-10% of overall construction cost and should be added to the budget instead of being created by trimming it. It also describes a planned drawdown: about 20% of the original design contingency used in the design phase, about 30% by design development and 50% or less in construction documents.

Other sources give a phase-based curve. Non-official study guides and a ConstructConnect article show roughly these ranges:

These bases differ from AIA's overall 5-10%, so you cannot average them. Choose one convention, document it, and apply it consistently. Sample contract language also shows design contingency being reduced at design development approval and at 50% and 90% construction-document estimates.

How much owner and construction contingency is typical?

Published examples show how varied the figures are.

• Utah State Capitol example (AIA): an owner contingency of 6%, built from 3% for scope, 2% for risk and 1% for politics.
• Design-build contractors (AIA): a contingency of 5-10% is common.
• Colorado Office of the State Architect (April 2022): construction contingency of 3% of the GMP for CM/GC and 3.5% for design-build with a GMP, plus a bidding contingency of 2.5% of the GMP.
• Western Michigan University facilities: capital project contingency typically 5-15% of the budget, depending on size and character.
• School-district example: one capital-project table lists owner contingency of 5% as a minimum for minor projects and 1% each for design and construction on major projects.

AIA also notes that most errors and omissions amount to less than 5% of a project's budget. That is useful context for sizing the owner's reserve, but it is a general observation, not a rule.

How should contingency change for renovation projects?

Hidden conditions drive renovation risk: unknown framing, asbestos or lead, deteriorated utilities, and structural surprises behind finishes. ConstructConnect's guidance puts renovation or projects with major unknowns at 10-15% or more, compared with 3-5% for a new building with complete, coordinated construction documents.

Reduce the unknowns before you finalize the reserve. Intrusive investigations, hazardous material surveys and as-built verification convert unknowns into line items.

A worked example: contingency through the phases

Illustrative example: a 40,000 SF two-story medical office building in Phoenix has an assumed base construction estimate of $24 million at schematic design. These numbers are assumptions to show the arithmetic.

If the base estimate holds steady, the reserve shrinks by $1.68 million between schematic design and construction documents. That money is not saved automatically. Either it covers real growth in the estimate, or it returns to the owner. Separately, the owner would still hold a construction-phase contingency (for example, an assumed 3-5% of the contract) for the period after bid.

How should contingency be approved and tracked?

A reserve only works if its use is visible. Agree on rules before the first draw.

• Approval. Define who can authorize a transfer from contingency to a line item, and the dollar threshold above which the owner signs.
• Reporting. Require a monthly log showing the original balance, each transfer, the reason, and the remaining balance.
• Purpose. Contingency should fund unforeseen conditions and design gaps, not owner upgrades. Upgrades are scope changes that need a budget increase or an offsetting deduction.
• Release. Tie the return of design contingency to milestones, such as design development approval and 50% and 90% construction-document estimates.

The link to change orders is direct. A change order that is funded from contingency should be recorded in both places, so the contingency balance and the contract sum always agree. Without that discipline, owners lose track of how much protection is left, often at the point when the largest changes arrive.

Why not just use a fixed percentage?

AACE's recommended practice 40R-08 is a guideline, not a standard, and gives a framework for estimating contingency. AACE's related practices cover range estimating with Monte Carlo simulation (41R-08) and parametric methods (42R-08). The consistent message is to quantify risk where you can and avoid relying on a flat percentage.

A simple version for owners: list the top 10 risks (soil, utilities, permitting, supply chain, scope growth), assign each a probability and a cost range, and sum the expected values. The result gives you a risk-based figure to compare with the rule-of-thumb percentage. If the two differ by more than a few points, investigate which risks the percentage is missing or double-counting, and document why you chose the number you carry. Lenders and boards respond better to a reasoned reserve than to an unexplained round number.

What happens if you carry too little?

A thin contingency forces an owner to find money after the contractor is committed. The options are all unwelcome: reduce scope, ask for more funding, or accept lower quality. Too much is also costly, because capital sits idle and discipline loosens.

An owner's checklist:

1. Define which of the three contingencies the budget holds.
2. State the percentage, the base it applies to and the date.
3. Write down who approves each use and how it is reported.
4. Plan the release schedule by phase.
5. Specify who keeps unused contingency at completion; many CM/GC agreements return it to the owner, but confirm yours.
6. Review how contingency interacts with allowances so the same risk is not covered twice or missed.

Remember that the percentages in this article are benchmarks from varied sources and bases. Costs and risks vary by market and project, so size your reserve from a project-specific risk review.