Cost-Plus Calculator
Apply a builder fee percentage to project cost, then calculate GST.
Result
- Builder fee
- $20,000.00
- Total ex GST
- $120,000.00
- GST
- $12,000.00
- Total inc GST
- $132,000.00
FREE COST-PLUS BUILDING CALCULATOR
Cost-Plus Calculator
Calculate a preliminary cost-plus amount by applying a builder margin to the entered project cost and then showing the GST-inclusive total where applicable.
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When this tool is useful
Practical preliminary checks
- Checking simple cost-plus pricing arithmetic
- Reviewing a builder margin against a nominated cost base
- Understanding the effect of margin and GST on a project cost
- Cross-checking preliminary variation or subcontractor calculations
How it works
The calculator applies the entered builder percentage to the nominated cost base, adds that amount to the cost, and then calculates the GST-inclusive total where selected.
Important estimating note
A cost-plus building contract is governed by its actual contract terms. This calculator does not determine which costs are chargeable, how margin applies under a particular contract, or the legal and tax treatment of a transaction.
Frequently asked questions
What is a cost-plus building contract?
In broad terms, actual project costs are charged under the contract and a builder fee or margin is added according to the agreed contract terms.
How is builder margin calculated in this tool?
The entered percentage is applied to the nominated cost base. The contract should be checked to confirm which costs the margin applies to.
Does the calculator replace the contract?
No. It is a simple arithmetic aid. The signed contract determines the actual charging method, eligible costs, margin and payment obligations.
Related EBC guidance
Understand the project behind the calculation
Need help applying the numbers to a real building project?
EBC works on renovations, extensions and new builds across Melbourne's Eastern Suburbs.