How to use this calculator
- Enter or choose base cost estimate.
- Enter or choose design contingency.
- Enter or choose construction contingency.
- The total budget updates as you type. Use Copy result or Share to keep it.
Method
Design = Base × d; Construction = Base × c; Budget = Base + Design + Construction
- Base
- estimated cost without contingency
- d, c
- design and construction contingency percentages
Worked example
- Design contingency = 800,000 × 5% = 40,000.
- Construction contingency = 800,000 × 10% = 80,000.
- Budget = 800,000 + 120,000 = 920,000; 120,000 ÷ 920,000 = 13.04%.
An 800,000 base with 5% design and 10% construction contingency gives a 920,000 budget.
What the result means
Draw down design contingency as the design firms up and construction contingency as risks materialise. Unused contingency should be released, not absorbed into scope.
Assumptions and limits
- Both percentages apply to the base cost.
- A flat percentage is a rule of thumb; a quantified risk register gives a better-founded figure for large projects.
Questions
What percentage should I use?
It depends on how complete the design is and how risky the work is. Ask your cost consultant or use your organisation’s guidance; the defaults here are examples only.
Should escalation be part of contingency?
Keep it separate. Use the Construction Cost Escalation Calculator for price changes over time.
Please note: Quantities are estimates. Confirm requirements with your engineer or supplier before ordering materials.