To fill out Form T661, you complete ten parts covering who you are, each SR&ED project you’re claiming, and the money you spent on that work; you then attach it to your income tax return along with the corresponding investment tax credit schedule and file within 12 months of your return’s due date. The form combines a technical narrative describing the research with a financial calculation of what it cost, and both halves have to hold up on their own.
Before You Open the Form
Three things need to be settled before you start typing into T661: whether your work qualifies, what records you have to back it up, and which overhead method you’ll use for the year.
Confirm the Work Qualifies
SR&ED covers basic research, applied research, and experimental development as defined in subsection 248(1) of the Income Tax Act. Experimental development — work aimed at a technological advancement to create or improve materials, devices, products, or processes — is what most claimants file under. Supporting work in engineering, design, computer programming, data collection, and testing counts too, as long as it directly supports one of the three categories and is carried out in Canada.1Canada Revenue Agency. Guidelines on the Eligibility of Work for Scientific Research and Experimental Development (SR&ED) Tax Incentives
Run each project through the CRA’s five-question test before you write anything, because the reviewer will:
- Was there a scientific or technological uncertainty?
- Did you formulate hypotheses specifically aimed at reducing or eliminating that uncertainty?
- Was your approach consistent with a systematic investigation, including testing hypotheses through experiment or analysis?
- Was the work undertaken for the purpose of achieving a scientific or technological advancement?
- Did you keep a record of the hypotheses tested and the results as the work progressed?
A “no” on any of the five is a strong signal the project will be denied on review.2Canada Revenue Agency. Eligibility of Work for SR&ED Investment Tax Credits Policy
Some activities are excluded outright, no matter how technical they look: market research or sales promotion, quality control or routine testing, social sciences and humanities research, prospecting and drilling for minerals or petroleum, commercial production of a new or improved product, style changes, and routine data collection. The commercial production line is the one that trips people up. Once you shift from figuring out whether something works to producing it for customers, the work stops qualifying, even if you’re still solving occasional problems along the way.3Canada Revenue Agency. Scientific Research and Experimental Development (SR&ED) Tax Incentives – Eligibility
Pull Your Records Together
The technical sections demand contemporaneous evidence of the uncertainty, the hypotheses, and the results. Laboratory notebooks, design documents, version control logs, meeting minutes, test protocols, and raw data all serve. Reconstructing the record from memory is visible to experienced reviewers.
The financial sections need payroll records showing which employees worked on SR&ED and for how many hours, invoices for materials consumed or transformed during experiments, and contracts with any subcontractors. If you go with the traditional overhead method, you also need documentation for every indirect cost you plan to claim.
Keep all supporting records for at least six years from the end of the last tax year they relate to. If you file late, the six-year clock starts from the date you actually file.4Canada Revenue Agency. Where to Keep Your Records, for How Long and How to Request the Permission to Destroy Them Early
Pick Your Overhead Method
You have to choose between the proxy method and the traditional method before entering expenditures, and the choice is binding for the entire tax year once you file. You cannot switch after submission.5Canada Revenue Agency. Traditional and Proxy Methods Policy
Under the proxy method, overhead is calculated automatically as 55% of your salary base (the portion of employee salaries attributable to SR&ED work). You don’t track or document individual overhead items like rent, utilities, or equipment maintenance. The resulting figure, called the prescribed proxy amount, replaces actual overhead in your qualified expenditure calculation and is used only for computing the investment tax credit.6Canada Revenue Agency. Prescribed Proxy Amount Policy
The traditional method lets you claim actual overhead, but every cost must be specifically identified, allocated, and documented: the share of rent for lab space, the portion of utilities consumed by research equipment, maintenance costs for SR&ED-specific facilities. On review, the CRA will ask for receipts and allocation methodologies for every line item. For most small and mid-sized companies, proxy is the practical choice. The traditional method wins clearly only when actual overhead significantly exceeds 55% of SR&ED salaries and you have detailed records for every dollar.
Part 1: General Information
Enter your legal name, business number, tax year start and end dates, and primary contact information. This section is straightforward, but a wrong business number or mismatched tax year here delays processing of the entire return.
Part 2: Project Information
You complete Part 2 once for each project you’re claiming in the tax year. It has three sections.7Canada Revenue Agency. T4088 – Scientific Research and Experimental Development (SR&ED) Expenditures Claim – Guide to Form T661
Section A: Project Identification
Enter the project title, internal project code if you have one, start and end dates, and the CRA field-of-science classification code from the appendix to the form. Indicate whether the project continues from a prior year and whether any work was performed jointly with another entity. If you’re claiming a multi-year project, use the same title consistently across years.
Section B: Technical Narrative
This is where claims are won or lost. Section B has three fields with strict word limits, and a CRA research and technology advisor with a science or engineering background will read them. Skip marketing language.
- Line 242 (350 words maximum): Describe the scientific or technological uncertainty. Explain the specific problem that could not be resolved using publicly available knowledge or standard practice. “We needed a faster product” isn’t an uncertainty. “The existing sintering process could not achieve particle density above 94% without cracking at the grain boundary” is.
- Line 244 (700 words maximum): Describe the work you performed. Walk through the hypotheses you tested, the experiments or analyses you conducted, and the results, in roughly chronological order. Use most of the space. Vague summaries like “we ran extensive tests” waste room and invite scrutiny.
- Line 246 (350 words maximum): Describe the advancement achieved. Identify the new knowledge or capability that resulted, even if the project did not reach its original goal. A failed experiment that taught you something about the material’s behavior still counts.
Section C: Additional Project Information
Identify who prepared the technical descriptions and their qualifications, name up to three key technical staff who worked on the project, indicate whether any work was performed outside Canada, list subcontractors involved, and describe what supporting documentation is available. The “outside Canada” question matters because only work carried out in Canada qualifies for the credit under the supporting-work provisions.
Parts 3 Through 5: Calculating Expenditures
Once you’ve made the overhead-method choice above, Parts 3 through 5 handle the numbers. The eligible categories are the same either way:
- Salaries and wages for employees who directly performed or supervised SR&ED work, prorated to reflect the time actually spent on eligible activities.
- Materials consumed or transformed during experiments. Materials that remain usable after the research concludes are not eligible.
- Payments to arm’s-length subcontractors for SR&ED work, though only a portion of the payment may qualify depending on the arrangement.
- Capital expenditures made after December 15, 2024, for equipment and other capital items used primarily for SR&ED. Capital expenditures had been excluded since 2014 and are now eligible again.
Line up salary costs with the project timelines you described in Part 2. If a project ran from March to September but you claim a full year of an employee’s salary against it, the discrepancy surfaces quickly in review.
How the Rate Applies to Your Total
Your entity type determines the credit rate that runs off these expenditure figures. Canadian-controlled private corporations earn a 35% fully refundable credit on the first $6 million in qualifying current expenditures for tax years beginning on or after December 16, 2024, with 15% on spending above the limit.8Government of Canada. Tax Measures: Supplementary Information – Budget 2025 Eligible Canadian public corporations can also earn 35% on the first $6 million, with phase-out based on prior three-year average gross revenue. Other corporations earn a flat 15% non-refundable credit. Individuals, partnerships, and trusts earn 15% with 40% of that credit refundable.9Canada Revenue Agency. SR&ED Investment Tax Credit Policy Capital expenditures within the CCPC expenditure limit earn 35% with 40% refundability on the capital portion.10Canada Revenue Agency. SR&ED Capital Expenditures Policy
Filing the Completed Form
Form T661 is not filed on its own. Attach it to your annual income tax return for the year the expenditures were incurred:11Canada Revenue Agency. SR&ED Filing Requirements Policy
- Corporations file with the T2 Corporation Income Tax Return.
- Individuals file with the T1 Income Tax and Benefit Return, plus Form T2038(IND) to claim the investment tax credit.
- Trusts file with the T3 Trust Income Tax and Information Return.
Corporations must also file Schedule T2SCH31 (Investment Tax Credit — Corporations) to actually claim the credit calculated from the T661 figures. Filing the T661 alone without the corresponding ITC schedule means you have reported your expenditures but not claimed the credit.
Associated Corporations
If your corporation is associated with other Canadian-controlled private corporations, the entire group shares a single $6 million expenditure limit for the enhanced 35% rate. The group files Schedule T2SCH49 to allocate the limit among its members. If no agreement is filed, each corporation’s expenditure limit defaults to nil, meaning nobody in the group gets the enhanced rate, until the CRA receives the allocation or imposes one itself.
Electronic vs. Paper
Most claims go in electronically through tax preparation software. If you use software to prepare and transmit your return, do not also send a paper copy of the T661; the CRA explicitly warns against duplicate submissions. Paper filing remains available for those who don’t file electronically.
The Deadline You Cannot Miss
The SR&ED reporting deadline is 12 months after your income tax return filing due date. Measured from the end of your tax year, the effective deadline works out to:
- Corporations: up to 18 months after the end of the tax year (6-month filing deadline plus 12 months).
- Individuals: up to 17½ months after the end of the tax year.
- Trusts: up to 15 months after the end of the tax year.
Miss it and the expenditures and related investment tax credits for that year are gone. The CRA does not grant extensions for late SR&ED claims, and there is no provision to file an amended return to add SR&ED expenditures after the reporting deadline has passed.
Mistakes That Sink Otherwise Valid Claims
A handful of errors show up again and again in denied or reduced claims.
Writing the technical narrative in business language rather than technical language is the single most common failure. “Developing a next-generation platform to improve customer experience” tells a reviewer nothing about scientific uncertainty. Describe the specific technical problem, the experiments, and the results.
Claiming hours that crossed into commercial production is another frequent problem. The moment your team shifts from resolving uncertainty to producing a product for sale, the time stops qualifying. Track the transition point in your timesheets.
Failing to keep contemporaneous records leaves you exposed even when the work genuinely qualified. The fifth eligibility question asks whether you recorded hypotheses and results as you went, and reconstructed records read as reconstructed.
Overlooking the associated-corporation allocation is an expensive administrative error. Without Schedule T2SCH49, every member’s expenditure limit drops to zero and the enhanced rate is off the table until the allocation is sorted out.