Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Estimated contract sum
$2,016,000
GC fee
$216,000
Contractor's share of savings under GMP
$92,000
Owner's share of savings under GMP
$92,000
Contractor-absorbed overrun above GMP
$0
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How to use this
- 1Enter estimated cost of work ($).
- 2Enter fee structure.
- 3Enter fee percentage (%).
- 4Enter flat fee amount ($).
- 5Enter gmp cap (0 = no cap) ($).
- 6Enter actual cost realized ($).
- 7Enter owner's share of savings below gmp (%).
- 8Read your estimated contract sum on the right — it updates as you type.
- 9Hit Share to keep the scenario or send it to someone.
About this calculator
Cost-plus-fee contracts pay the contractor their actual verified cost of the work plus a negotiated fee, commonly structured as a flat fee or a percentage of cost, often with a guaranteed maximum price (GMP) cap that shifts overrun risk back to the contractor above that ceiling while sharing savings below it. This calculator computes GC fee under either a percentage-of-cost or flat-fee structure, adds it to estimated cost of work to produce the total contract sum, and applies a GMP cap if one is negotiated, showing the contractor's exposure if actual cost exceeds the cap. It also models a savings-share clause, common on GMP contracts, where cost coming in under the GMP is split between owner and contractor at an agreed percentage, which is a meaningful incentive-alignment tool worth understanding before you negotiate the split ratio.
Worked example
Using the values the calculator loads with:
Inputs
- Estimated cost of work: 1800000 $
- Fee structure: Percentage of cost
- Fee percentage: 12 %
- Flat fee amount: 200000 $
- GMP cap (0 = no cap): 2100000 $
- Actual cost realized: 1700000 $
- Owner's share of savings below GMP: 50 %
Results
- Estimated contract sum: $2,016,000.00
- GC fee: $216,000.00
- Contractor's share of savings under GMP: $92,000.00
- Owner's share of savings under GMP: $92,000.00
- Contractor-absorbed overrun above GMP: $0.00
What each field means
Inputs
- Estimated cost of work ($)
- The estimated cost of work used in the calculation, measured in $. Starts at 1800000 $ so you have a working example on load.
- Fee structure
- Pick the option that matches your situation — the maths changes per option. Choices: Percentage of cost, Flat fee.
- Fee percentage (%)
- The fee percentage used in the calculation, measured in %. Starts at 12 % so you have a working example on load. Accepted range: 0–30 %.
- Flat fee amount ($)
- The flat fee amount used in the calculation, measured in $. Starts at 200000 $ so you have a working example on load.
- GMP cap (0 = no cap) ($)
- The gmp cap (0 = no cap) used in the calculation, measured in $. Starts at 2100000 $ so you have a working example on load.
- Actual cost realized ($)
- The actual cost realized used in the calculation, measured in $. Starts at 1700000 $ so you have a working example on load.
- Owner's share of savings below GMP (%)
- The owner's share of savings below gmp used in the calculation, measured in %. Starts at 50 % so you have a working example on load. Accepted range: 0–100 %.
Results
- Estimated contract sum
- Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- GC fee
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Contractor's share of savings under GMP
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Owner's share of savings under GMP
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Contractor-absorbed overrun above GMP
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
What fee percentage is typical for a cost-plus-GMP contract?
Commercial GC fees on cost-plus-GMP contracts commonly run 5-15% of cost depending on project complexity, risk, and market competitiveness, with straightforward repeat-design work at the low end and complex, high-risk, or fast-tracked projects at the higher end. Fee percentage should reflect the actual risk the contractor is absorbing, which is why a hard GMP cap often justifies a slightly higher fee than pure cost-reimbursable with no cap.
Why would an owner prefer a percentage fee over a flat fee?
Actually the opposite is usually true from the owner's perspective — a percentage-of-cost fee gives the contractor a perverse incentive to let costs run higher since their fee grows with cost, while a flat fee removes that incentive and aligns the contractor toward genuine cost control. Sophisticated owners frequently push for flat fee structures on cost-plus work specifically to avoid this misalignment.
How does the savings split incentivize the contractor under a GMP?
If the contractor keeps 50% of savings below the GMP, they're financially motivated to find real cost efficiencies since half the benefit flows to their own bottom line rather than 100% going to the owner. Splits commonly range from 50/50 to 80/20 in the owner's favor, with the exact ratio negotiated based on how much of the savings potential came from the contractor's expertise versus a padded initial GMP.
What happens to the fee itself if actual cost exceeds the GMP?
The fee is typically locked in at the amount calculated from the original estimated cost (or sometimes recalculated on the GMP itself), and does not grow if actual cost overruns — the contractor absorbs the overrun in cost, not fee, which is exactly the risk-shifting mechanism a GMP is designed to create. Confirm this explicitly in contract language since ambiguous fee-recalculation clauses are a common source of GMP disputes.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
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Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). General Contractor Fee Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/general-contractor-fee-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/general-contractor-fee-calculator" target="_blank" rel="noopener">General Contractor Fee Calculator — RevenueLab</a> (2026).</p>
Source: [General Contractor Fee Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/general-contractor-fee-calculator) (2026).