Estimating

Change Orders: T&M vs. Lump Sum — Which Actually Makes Money

Every project manager has priced a change order two ways — one on AIA G701 with a fixed number, one on T&M with a rate sheet — and watched the same scope come in thousands apart. The method you pick is not about speed. It is about who owns the productivity risk, whether the scope is clearly defined, and how long the approval is going to take.

Amelia Frost Principal, Frost Construction Consulting
April 9, 2026 12 min read

AIA G701 and what the form actually asks for

AIA Document G701-2017 Change Order is the standard instrument for formal contract modification in contracts on AIA A101/A201 forms. It captures the change in contract sum, the change in contract time, and the revised totals, and it is executed by the owner, architect, and contractor. Before G701 is signed, the pricing arrives on a Proposal Request response or on the contractor's Change Order Request (COR) with a back-up breakdown.

The form does not specify method. It accepts a lump sum (one dollar figure, one signature, done) or T&M billed against a rate schedule. The choice — lump sum, T&M, unit price, cost-plus with GMP — should be called out in the supporting back-up. What A201 Section 7 does specify is the allowable markup ranges and the categories of recoverable cost. Read A201-2017 Section 7.3.7 for the overhead-and-profit categories specifically.

When lump sum actually wins

Lump sum pricing beats T&M when:

Under those conditions, a contractor who prices the change correctly keeps every dollar of the productivity premium. If the take 4 hours estimate turns into 3 hours of field time, the extra hour is margin.

When T&M actually wins

T&M wins when scope is undefined or fluid, the work disrupts the base contract, the contractor cannot estimate productivity with confidence, or the owner's RFI loop is unpredictable. T&M billing covers actual hours, actual material with a markup, and equipment actually used. The owner takes the productivity risk — if the work takes 40% longer than anyone expected, the contractor is paid for every hour.

The tradeoff: T&M ceilings get scrutinized harder at billing. Daily tickets have to be signed by the owner's representative or architect. If you fail to get signatures or fail to capture the full burden on the rate sheet, unbilled hours evaporate.

Composite crew rate for change orders

Whichever method you use, the crew rate calculation is the same and it matters. A clean composite rate for a change order includes:

The formula:

Composite Rate = (Base Wage + Fringe) × (1 + Statutory% + Insurance%) + Small Tools + Supervision Share + OT Premium

Allowable overhead and profit markups

Industry-standard overhead and profit markups for change orders, based on widely-published contracts and historical AGC/ABC surveys:

Contract TierOverhead %Profit %Typical Combined
General Contractor on own forces10-12%5-7%15-19%
General Contractor on subcontracted scope5-7%3-5%8-12%
First-tier Subcontractor12-15%8-10%20-25%
Second-tier Subcontractor10-12%5-8%15-20%
Bond, when required1.0-1.5%1.0-1.5%
Insurance (GL / umbrella)0.8-1.5%0.8-1.5%

Some contracts cap total markup stack (GC + sub + sub-sub) at a number — 25% is common, 30% generous, 20% tight. Always check A201 Section 7.3.7 or the project-specific supplementary conditions before quoting.

Productivity loss and the MAA method

When a change order disrupts ongoing base-contract work, you are entitled to claim lost productivity — the hours that would have been billed to the base contract but ran slower because of the change. The industry-accepted framework is the Measured Mile method, published in detail in Ibbs and Nguyen's Construction CPM and Schedule Risk Analysis literature and AACE International's Recommended Practice 25R-03 on Estimating Lost Labor Productivity.

Measured Mile compares productivity on an unimpacted section of identical work with productivity on the impacted section. The delta, converted to inefficient manhours, becomes a claim. If unimpacted base-contract conduit runs 2.8 mh per 100 LF and the same work post-change-disruption runs 3.9 mh per 100 LF, the lost-productivity factor is (3.9 − 2.8) / 2.8 = 39%. That 39% applied to affected base-contract hours is a real, documentable claim.

The alternative, MCAA-factor method (also the NECA Column 3 approach), applies a published inefficiency percentage to the impacted scope — typically 10-30% depending on the disruption type. It is weaker evidentially but widely accepted when measured-mile data does not exist.

Common Bid Mistake

Quoting a lump-sum change order during an active owner-directed delay without protecting productivity loss on unimpacted work. The lump sum signed on AIA G701 typically includes a broad waiver of further claims related to the change. Sign it, and you have signed away the measured-mile claim on the base-contract inefficiency caused by the same change. Always carry T&M or include explicit productivity-impact reservation language.

Contingency vs. allowance — two different animals

Both appear in change-order discussions and they are not interchangeable. A contingency is owner-controlled money set aside for unknowns; it is released at the owner's direction and typically requires an owner-approved change order to draw against. An allowance is a contract-sum carrying amount for a scope defined in concept but not in detail (hardware allowance, flooring allowance); when the actual scope is priced, a deductive or additive change order reconciles the allowance to actual cost per A201-2017 Section 3.8.

On contingency, the contractor has no claim until work is directed. On allowance, the contractor has a contractual obligation to propose and execute the scope within the allowance framework. Mixing the two in a COR conversation leads to arguments that are avoidable if the language was clean at contract signing.

Delayed approval and carrying cost

A change order sitting in architect or owner review for 90 days is costing the contractor money. Two categories of carrying cost apply:

The discipline: every open COR older than 45 days generates a carrying-cost line on the disputed change log, so the cumulative exposure is visible to ownership and recoverable if the change is ultimately executed.

The disputed change log

Every active project maintains a change log, but the discipline that separates profitable firms from break-even ones is the disputed change log — CORs submitted, CORs in review, CORs rejected, CORs approved but unexecuted. Each line carries the scope, dollar amount, date submitted, current age, and a flag for carrying-cost accrual. Monthly, this log feeds the WIP schedule and shows up on the risk report to ownership.

Without this discipline, disputed changes quietly become losses at project closeout when memory is poor and documentation is thin.

Worked example: 3-day T&M vs. lump sum

Scope: add two 30-amp circuits from a new subpanel to two new dedicated receptacles in a healthcare corridor, with existing ceilings to be reopened and reclosed. Scope is partially defined — circuit routing requires field verification above ceilings and coordination with base-building MEP.

Pricing ElementLump SumT&M (Actual)
Electrician hours (estimated)18 mhactual: 26 mh
Apprentice hours (estimated)18 mhactual: 26 mh
Composite rate electrician$115/hr$115/hr
Composite rate apprentice$78/hr$78/hr
Labor cost$3,474$5,018
Material — wire, conduit, devices, fittings$1,180$1,210 actual
Material markup at 15%$177$182
Small tools/consumables$95$118
Subtotal$4,926$6,528
Sub overhead & profit 22%$1,084$1,436
GC overhead & profit 10%$601$796
Change order total$6,611$8,760

Actual field time landed at 26 hours per trade rather than 18, driven by unexpected cable tray congestion above the corridor ceiling. On the lump sum, the sub absorbs the $2,149 overrun. On T&M, the owner pays it. Both invoices ride AIA G701. In both cases, the markup stack is 32% — the difference is who holds the productivity risk.

The operating principle

Quote lump sum when you own the productivity. Quote T&M when the owner owns the disruption. Never sign a G701 without reviewing the language for waiver of further claims, and always keep the disputed change log current so carrying cost is documented and recoverable. The firms that grow on change orders are the firms that run this discipline every week.

PILRS attaches change-order quantification to the takeoff so the same crew rates and burden stack from the base bid flow directly into the COR. See pricing and make the change-order conversation a pricing exercise, not a renegotiation.

Key Takeaways

What to carry into your next bid

  1. AIA G701 accepts lump sum, T&M, or unit price — the method determines who owns productivity risk
  2. Typical markups: GC 10-12%, sub 20-25%, stacked cap usually 25-30% per A201 Section 7.3.7
  3. Measured Mile (AACE 25R-03) is the strongest productivity-loss method; MCAA factors are the fallback
  4. Contingency is owner-controlled; allowance is contract-sum carrying per A201 Section 3.8 — do not confuse them
  5. Disputed change log with carrying-cost accrual every 45 days protects recovery under Eichleay and similar

Stop counting. Start reviewing.

PILRS turns the takeoff into a review step. See it on a real plan set from your next bid — free, no credit card.

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