What is a cost-plus construction contract?

A cost-plus contract pays the contractor for the actual cost of materials, labor, and subcontractors PLUS a fee — either a percentage of cost (cost-plus-percentage, typically 15-25%) or a flat fee (cost-plus-fixed-fee). The owner bears cost-overrun risk; the contractor has minimal incentive to control costs in pure cost-plus-percentage. Most modern cost-plus contracts add a Guaranteed Maximum Price (GMP) cap that converts the contract effectively to fixed-price above a threshold while preserving the cost-plus billing structure below it.

What is the markup percentage on a cost-plus contract?

Industry standard 2026 markup ranges: residential remodeling 15-25%, custom home builders 18-25%, commercial fit-out 12-18%, ground-up commercial 10-15%, design-build with architect coordination 20-25%. Markup covers contractor overhead (office, insurance, vehicle, software), profit margin (typically 8-15%), and supervision costs. NEVER pay markup on owner-supplied materials or owner-direct subcontractor invoices — that's double-dipping.

When should I use a fixed-price contract instead?

Fixed-price (lump sum) contracts work best when: (1) scope is fully designed and quantified BEFORE contract signing, (2) project duration is under 12 months (less time for material cost volatility), (3) site conditions are known (no excavation surprises), (4) owner has no scope flexibility budget. Risk shifts to contractor — they build in 8-15% contingency for unknowns. If actual cost runs lower than the lump sum, contractor profits more. If higher, contractor absorbs the loss (or attempts change orders for "additional work").

What is GMP (Guaranteed Maximum Price)?

GMP is a cap added to cost-plus contracts: contractor charges actual cost + markup but agrees the total will not exceed a guaranteed maximum. Below GMP: owner pays actual cost + markup. Above GMP: contractor absorbs cost. Hybrid contracts often share savings below GMP (e.g., 70% to owner, 30% to contractor as bonus). GMP requires contractor to do detailed pre-construction estimating; expect 1-3% pre-construction fee to develop the GMP. Most large commercial projects use GMP under AIA Document A102.

How are change orders handled in each contract type?

Cost-plus: change orders are billed at actual cost + agreed markup, no negotiation needed for execution but documented for audit. Fixed-price: change orders require WRITTEN agreement on scope, cost, and time impact BEFORE work begins — contractors typically charge premium markup (25-40%) on change orders because the buyer has no leverage at this point. AIA Document G701 is the standard change order form. Owners should require dual signatures and 48-hour notice on any cost over $500.

What owner protections should I require in a cost-plus contract?

Five non-negotiable owner protections: (1) Open-book accounting — contractor provides ALL receipts, invoices, time sheets monthly; (2) Audit rights — owner can audit books up to 1 year post-completion; (3) Approved subcontractor list — owner pre-approves subs; (4) Allowance items — specific line-item caps on uncertain costs (countertops, light fixtures, plumbing fixtures) with owner-approved overage; (5) Lien waivers — full waivers from contractor and all subs before progress payment release. NEVER pay invoices without these.

How does insurance differ between cost-plus and fixed-price?

General liability and workers comp are similar. Differences: (1) Builder's risk insurance is owner-paid in cost-plus (covered by owner's policy) vs contractor-paid in fixed-price; (2) Cost-plus often requires higher limits ($2-5M GL) because cost overruns expose owner to more liability; (3) Performance and payment bonds are MORE common in fixed-price (contractor at risk of non-completion). Always require certificates of insurance naming owner as additional insured. Verify directly with insurance carrier — fake COIs are a known fraud pattern.

Which contract is better for a kitchen remodel under $50K?

Fixed-price is usually best for projects under $50K with defined scope. Reasoning: (1) project duration is short (4-8 weeks) limiting material cost volatility, (2) scope is typically well-defined (cabinets selected, appliances chosen), (3) contractor markup overhead is similar regardless of contract type so no cost advantage to cost-plus, (4) administrative burden of tracking actual costs in cost-plus exceeds any savings. Use cost-plus for: full home renovations, additions affecting structural elements, projects requiring engineer redesigns mid-build.

Cost-Plus vs Fixed-Price Construction Contract 2026

Short answer: Choose fixed-price when scope is fully designed and project under 12 months — contractor builds in 8-15% contingency, you pay one number. Choose cost-plus when scope is unclear, complex, or evolving — actual cost + 15-25% markup, owner bears overrun risk. Add a Guaranteed Maximum Price (GMP) cap to cost-plus to limit downside. AIA Document A101 (lump sum) vs A102 (cost-plus with GMP) are industry standards.

Side-by-side comparison

Aspect	Cost-Plus	Fixed-Price (Lump Sum)
Risk allocation	Owner bears cost overrun risk	Contractor bears cost overrun risk
Typical markup	15-25% on actual cost	8-15% built into lump sum
Best for	Unknown scope, complex remodels, time-sensitive starts	Fully designed projects, short duration
Pricing transparency	Open book — owner sees every invoice	Sealed price — costs are contractor internal
Change order ease	Cost + markup, fast execution	Negotiated, often premium 25-40% markup
Cost incentive	Weak (without GMP) — markup grows with cost	Strong — contractor profit grows if costs drop
Pre-construction effort	Lower — start fast	High — full estimating, plans, specs
Owner administration	High — review invoices monthly	Low — pay scheduled progress payments
AIA template	A102 (cost-plus with GMP) or A103	A101 (lump sum)
Typical retainage	10% until 50% complete, then 5%	10% until substantial completion

2026 markup percentages by project type

Project type	Cost-plus markup	Fixed-price contingency
Residential remodeling (kitchen/bath)	15-22%	8-12%
Custom home builder (ground-up)	18-25%	10-15%
Whole-home renovation	20-25%	12-18%
Commercial fit-out (TI)	12-18%	6-10%
Ground-up commercial	10-15%	5-8%
Design-build (with architect)	20-25%	10-15%
Disaster restoration / insurance work	10-20% (capped by insurer)	N/A (T&M typical)

5 mandatory owner protections in cost-plus contracts

Open-book accounting. Contractor provides ALL receipts, invoices, time sheets monthly. Receipts must include item-level detail (not just lumped categories).
Audit rights. Contract clause allowing owner audit of books up to 1 year post-completion. Includes right to verify hourly rates against time sheets and material markups against vendor invoices.
Approved subcontractor list. Owner pre-approves all subs above $5K. Prevents contractor steering to favored subs at inflated rates.
Allowance items with caps. Specific line-item caps on uncertain costs (countertops $X/sf, light fixtures $Y, plumbing fixtures $Z). Overages require owner approval before purchase.
Lien waivers required at every payment. Conditional partial waiver with each invoice; unconditional waiver after payment clears. NEVER release a payment without waiver from contractor AND all subs paid from those funds.

Decision tree — which contract for your project?

Question 1: Is the design 95%+ complete with stamped plans?

→ Yes: continue to Q2. No: Cost-plus with allowances recommended.

Question 2: Will the project complete within 12 months?

→ Yes: continue to Q3. No: Cost-plus with GMP recommended (material price escalation risk).

Question 3: Is the project under $200K?

→ Yes: Fixed-price (lump sum) recommended. No: continue to Q4.

Question 4: Will site conditions or scope likely change?

→ Yes: Cost-plus with GMP recommended. No: Fixed-price with detailed change-order procedure.

Related Hammer.io resources

Sources: AIA (American Institute of Architects) Document A101, A102, A103 2017 editions, AGC (Associated General Contractors) Standard Contract Forms 2026, Construction Specifications Institute (CSI) MasterFormat 2024, RSMeans Heavy Construction Cost Data 2026 markup analysis. Markup percentages reflect 2026 industry surveys including JLC Live Builder Roundtable, BuilderTrend benchmark report, NAHB/Wells Fargo Builder Confidence Index. Always have construction contracts reviewed by a licensed construction attorney in your state — local laws on retainage, lien rights, and consumer protections vary significantly.