The R&D Tax Credit · Brief · Working level
The substantially-all rule: how 80% becomes 100% (or nothing)
Section 41's two 80% thresholds — the wage rule that credits an employee's full wages when qualified services reach 80%, and the business-component rule requiring substantially all activities to be elements of experimentation — plus shrink-back and a worked example.
Two different 80% thresholds share the name "substantially all," and confusing them is a standard exam-season error. One is generous: an employee whose qualified services reach 80% of total services gets all wages counted. One is demanding: a business component qualifies only if at least 80% of its research activities are elements of a process of experimentation — the test the taxpayer failed in Little Sandy Coal Co. v. Commissioner. Both use 80%; they run in opposite directions.
The wage rule: 80% rounds up to 100%
Treas. Reg. §1.41-2(d)(2) provides that where substantially all — 80% or more — of an employee's services are qualified services, all of the employee's wages for the year are wage QREs. An engineer at 85% research yields 100% of her wages; an engineer at 75% yields 75%. The cliff only helps: below the threshold you still claim the actual percentage.
The rule's audit shadow is predictable. Allocations that cluster at exactly 80% across a department look reverse-engineered, and examiners test them hard. Time records that show honest variation — 62% here, 91% there — substantiate the individuals who genuinely cross the line. What counts as qualified services in the first place is covered in qualified services and wages.
The component rule: 80% or the claim shrinks
Section 41(d)(1)(C) requires that substantially all of the activities of the research constitute elements of a process of experimentation, measured per business component. The regulations at eCFR Title 26 (Treas. Reg. §1.41-4(a)(6)) let taxpayers measure by cost or another consistently applied reasonable basis. Little Sandy Coal (7th Cir. 2023) made the consequence concrete: asserting a first-of-kind vessel was "experimental in its entirety," without allocating activities between experimentation and routine fabrication, failed for lack of proof — the 80% must be computed, not declared.
When a component fails, shrink-back (Treas. Reg. §1.41-4(b)(2)) reapplies the test at the next-smaller level — the drivetrain rather than the vehicle, the scheduling module rather than the ERP system — until some subset qualifies. The claim then covers research on that subset only.
Worked example
A machinery maker spends $1,000,000 developing a new packaging line (one business component). Activity analysis, by cost:
| Activity | Cost | Element of experimentation? |
|---|---|---|
| Concept design and alternative evaluation | $200,000 | Yes |
| Prototype build and iterative testing | $350,000 | Yes (including direct support) |
| Standard conveyor sections, catalog engineering | $300,000 | No |
| Installation and operator training | $150,000 | No |
Experimentation elements total $550,000 — 55%, well short of 80%. The full line fails. Shrink back to the novel filling head subassembly: its costs are the $200,000 design and $350,000 prototype work, of which, say, $500,000 (91%) are elements of experimentation. The subassembly passes, and the claim proceeds on its research costs — not the conveyor sections, not the training. Compare the all-or-nothing alternative: without shrink-back, the failed 55% would have zeroed the component.
The activity-level records that make this computation possible are the same ones described in the documentation playbook; the underlying qualification standard is the four-part test. The IRS research credit overview summarizes both thresholds without, unhelpfully, distinguishing them by name — the regulations do that work.
Frequently asked questions
- What is the substantially-all rule for R&D credit wages?
- Under Treas. Reg. §1.41-2(d)(2), if at least 80% of an employee's services for the year are qualified services — direct research, direct supervision, or direct support — then 100% of the employee's wages count as qualified research expenses. Below 80%, only the actual qualified percentage counts. The rule rounds up generously at the threshold but gives nothing extra below it.
- What is the substantially-all test for a business component?
- Section 41(d)(1)(C) requires that substantially all — at least 80%, measured by cost or another consistently applied reasonable basis — of a business component's research activities constitute elements of a process of experimentation. If the whole component fails, the shrink-back rule of Treas. Reg. §1.41-4(b)(2) applies the test to the next-smaller subset until a qualifying subcomponent is found.
- What is the shrink-back rule?
- Shrink-back, in Treas. Reg. §1.41-4(b)(2), rescues partial claims: when a whole product or process fails the four-part test's substantially-all requirement, the test is reapplied to the most significant subset of the component's elements — a module, a subassembly — and continues shrinking until a level qualifies. The claim then covers the qualifying subcomponent's research costs.