Construction Contract Types: Lump Sum, Cost-Plus, GMP, Time and Materials — When to Use Each

LUMP SUM (FIXED PRICE): contractor commits to perform defined scope for fixed dollar amount. Owner pays the fixed price regardless of contractor's actual cost. Best for: clearly defined scope, complete plans, owner wants price certainty. Risk on contractor (overruns are contractor's loss). COST-PLUS: owner pays contractor's actual costs plus a fee (fixed dollar or percentage). Best for: emergency work, evolving scope, custom work, demolition/renovation with unknowns. Risk on owner (overruns flow to owner). GMP (GUARANTEED MAXIMUM PRICE): hybrid — owner pays cost-plus up to a ceiling, then contractor absorbs overruns above the GMP. Best for: large complex projects, owner wants protection against runaway costs while preserving some open-book transparency. TIME AND MATERIALS (T&M): contractor bills hourly labor rates plus materials cost plus markup. Best for: small repairs, undefined scope, service calls. Risk on owner with hourly cap typical. This content is for educational purposes only and does not constitute legal or business advice.

Contractor commits to fixed dollar amount for defined scope. Contractor profit depends on accurate estimating — overruns reduce profit; under-runs increase it. Owner has price certainty for budgeting. Best for: residential remodels with complete plans, new construction with clear specs, projects where competitive bidding determines price. Pricing approach: detailed estimate with contingency built in (typical 5-15% contingency for moderate-risk projects, 15-25% for higher-risk or unclear scope). Lower contingency = more competitive bid but higher contractor risk. Higher contingency = safer but less competitive. The estimator's judgment on contingency level is critical.

Owner pays contractor's actual cost (labor, materials, sub costs) plus a fee. Fee structure: percentage (typical 10-20% on direct cost), fixed dollar amount, or sliding scale. Best for: emergency repairs (fire, flood), demolition with unknown conditions, custom high-end work, projects with multiple owner-driven design changes. Owner sees all invoices and can audit costs (open-book). Risk on owner: no price ceiling means actual cost can substantially exceed initial estimates. Contractor incentive issue: percentage fee structures incentivize higher cost (more fee). Fixed fee or capped percentage mitigates this. Common practice: combine cost-plus with a budget estimate and require owner approval for any work that would exceed budget.

Owner and contractor agree to a Guaranteed Maximum Price ceiling. Within the GMP, contractor bills costs plus a fee (like cost-plus, with full transparency). If actual costs exceed the GMP, the contractor absorbs the overrun (no additional billing). Most GMP contracts also include a SHARED SAVINGS clause: if actual costs come in under the GMP, the savings are shared between owner and contractor (typically 50/50 or 70/30 in owner's favor). Best for: large complex commercial or institutional projects, owner wants protection but values open-book transparency. Pricing: contractor builds a detailed estimate, adds contingency (typical 8-15%), sets GMP at estimate + contingency. The contractor accepts substantial cost overrun risk; the markup typically reflects this risk (15-25% combined contingency + fee).

Contractor bills hourly labor rates (fully-loaded with burden, overhead, and profit) plus materials at cost or with markup (typical 15-25%). Hourly rates are typically posted in the contract. Owner pays as work proceeds, with invoices itemized by hour and material. Best for: service repairs (plumbing repair, HVAC service), small remodels with unclear scope, change orders where amount is small. Risk on owner: unlimited cost exposure unless capped (most T&M contracts include a "not-to-exceed" amount with owner approval required to exceed). Common rates: $75-150/hr for general contractor; $100-200/hr for licensed trades; materials marked up 15-25%. Submit detailed time logs with invoices.

Decision criteria: (1) Is the scope clearly defined? Yes → lump sum or GMP. No → cost-plus or T&M. (2) How much risk can the owner accept? Low risk → lump sum (owner has price certainty). Medium → GMP. High risk acceptance → cost-plus or T&M. (3) Project size? Small repairs/service → T&M. Medium projects → lump sum or T&M. Large complex projects → GMP. (4) Is the owner willing to pay for transparency? Yes → cost-plus or GMP (open book). No → lump sum. Most residential remodel contracts are lump sum because owners want price certainty. Most large commercial projects use GMP because of complexity. Most service work is T&M. Custom luxury work often uses cost-plus.

ContractorIQ does not choose a contract type or generate contracts. Whatever type you use, the estimate behind it starts the same way: photograph or describe the job, and ContractorIQ itemizes the materials and labor with the assumptions behind the total. Its estimator can explain how lump sum, cost-plus, GMP, and time-and-materials pricing differ, and a construction attorney should review the contract itself. This content is for educational purposes only and does not constitute legal or business advice.