Estimating with missing information and provisional allowances.
No project has complete information at tender stage. Provisional allowances and risk provisions let you price the known work while protecting against the unknown.
Who this guide is for
Estimators pricing tenders with incomplete drawings or specifications, contractors managing risk, and quantity surveyors preparing cost plans with design stage allowances.
Types of allowance
Provisional sum: An amount included for work that cannot be fully defined. The client or architect will decide later.
Risk allowance: Covers specific risks identified in the project risk register — ground conditions, price inflation, weather delays.
Contingency: A general allowance for unforeseen items, typically 5–15% depending on project stage.
Design development allowance: For elements where the design is not yet finalised, such as kitchen fit-out or specialist lighting.
Miniature example
A warehouse extension at £480,000 includes: provisional sum of £25,000 for mechanical ventilation (design not final), risk allowance of £15,000 for potential ground improvement (based on trial hole indications), and contingency of £40,000 (approximately 8%). Total with allowances: £560,000.
Common mistakes
- Including a provisional sum without stating what it covers — the client does not know what is missing
- Using a single blanket contingency instead of identifying specific risks
- Omitting allowances entirely to make the tender look cheaper — the cost will emerge as variations
Related guides and tools
Learn about assumptions and exclusions and variations and change orders. Use the Budget Estimate generator to include contingency.