Top 10 Common Mistakes to Avoid When Claiming the US R&D Tax Credit

  • By Ichrak El Missaoui
    • Mar 24, 2026
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Claiming the Section 41 Research Tax Credit can significantly boost your company’s cash flow. However, the IRS maintains strict standards for eligibility and documentation. Small errors in your application can lead to delays or audits. To ensure your claim stands up to scrutiny, here are the top 10 mistakes you should watch out for when applying for R&D in the US.

Failing the Four-Part Test

Every activity must meet the IRS “Four-Part Test” to qualify. You must prove the work is for a permitted purpose, involves elimination of uncertainty, includes a process of experimentation, and is technological in nature. If one part is missing, the entire activity is ineligible.

Including Non-Technical Roles

The IRS focuses on “qualified services.” This includes those performing, supervising, or supporting research. High-level executives or administrative staff who are not directly involved in the technical experimentation should generally be excluded from the wage calculation.

Neglecting “Funded Research” Rules

If a third party pays you to perform R&D and you do not retain substantial rights to the results, you cannot claim the credit. Similarly, if you do not bear the financial risk of failure, the research is considered “funded” by the client and is ineligible for your claim.

Insufficient Documentation

The IRS requires “contemporaneous records.” This means you must provide documentation created during the research process. Relying on end-of-year oral testimonies or vague summaries often leads to denied claims during an audit.

Claiming “Adaptation” as Innovation

Adapting an existing product to a specific client’s needs is not necessarily R&D. If the solution was already available through standard engineering practices or public knowledge, it does not meet the “technological uncertainty” requirement.

Overlooking the Discovery Rule

While you don’t need to invent something new to the world, the work must be new to your company. You must demonstrate that your team moved beyond existing internal knowledge to develop a new or improved function, performance, or quality.

Inaccurate Wage Allocations

Estimating percentages of time spent on R&D without supporting data (like time logs or project-based tracking) is a major red flag. Over-allocating time for employees who only have peripheral involvement can trigger an IRS review.

Missing “Supply” Definitions

Only tangible property used in the R&D process (like prototypes or chemicals) qualifies. General administrative supplies, travel expenses, and depreciable property (like computers or lab equipment) are strictly excluded from “qualified research expenses.”

Misunderstanding the Internal Use Software (IUS) Rule

If you are developing software for internal administrative use, the standards are much higher. You must prove the software is innovative, involves significant economic risk, and is not commercially available.

Ignoring State-Level Credits

Many US states offer R&D credits that mirror the federal Section 41 credit. Failing to align your state and federal applications can result in missed savings. Always check for specific state requirements, as they may offer different carry-forward or refundability options.

To dive deeper into optimizing your R&D tax credit strategy and avoiding these costly mistakes, download our comprehensive US R&D guide and turn potential risks into maximized savings.

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ichrak el missaoui
Ichrak El Missaoui

Digital Marketing Executive

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