If your agency builds custom Klaviyo flows for clients, you have probably wondered whether the development time qualifies for R&D tax credits. The short answer is: yes, it can. But only for specific types of work. And the line between qualifying R&D and routine development is sharper than most agency founders realise.

This article explains exactly where that line sits. We will walk through what HMRC actually looks for in a klaviyo custom flow r&d claim, what almost certainly does not qualify, and how to structure your records so you do not waste time on a claim that gets rejected.

What HMRC Considers R&D in Software Development

HMRC follows the Guidelines on the Meaning of Research and Development for Tax Purposes (the BEIS guidelines). For software work to qualify, the project must seek to achieve an advance in science or technology. That advance must be in the field of software engineering, not in the client's business processes.

In plain English: you need to have attempted something that a competent professional in your field would not know how to do at the start of the project. If the solution was obvious or already documented, it is not R&D.

For Klaviyo specifically, the test is whether your team had to resolve technical uncertainty. Did you need to create a novel integration, build a custom data pipeline that Klaviyo does not natively support, or develop a scoring algorithm that required genuine experimentation?

If you simply configured standard Klaviyo triggers, conditions, and actions, that is skilled work. But it is not R&D.

What Qualifies as a Klaviyo Custom Flow R&D Project

Let me give you a concrete example from a real claim we submitted for a digital agency based in Manchester's Northern Quarter. They had a client in the subscription box space. The client needed a flow that could predict churn risk based on 14 behavioural signals, then dynamically adjust email frequency, content type, and discount thresholds in real time.

Klaviyo does not natively support multi-variable predictive scoring with dynamic content branching based on real-time data ingestion from three separate APIs. The agency had to build a custom middleware layer in Node.js, write a scoring algorithm from scratch, and create a feedback loop that updated the model as new data came in. They tested 11 different approaches before one worked reliably at scale.

That is R&D. The team faced genuine technical uncertainty. They did not know at the outset whether the approach would work. They documented their hypotheses, their failed attempts, and the eventual solution. HMRC accepted the claim.

Other examples that can qualify:

  • Building a custom attribution model that pulls data from Klaviyo, Google Ads, Facebook, and an offline sales CRM, then reconciles them into a single customer view. Standard Klaviyo attribution is limited. If you need to build a custom solution because no off-the-shelf tool exists, that is technical uncertainty.
  • Developing a bespoke personalisation engine that uses machine learning to select product recommendations based on browsing behaviour, past purchases, and real-time inventory. Klaviyo's built-in product recommendations are rule-based. If you are building something genuinely adaptive, you may have a claim.
  • Creating a custom A/B testing framework that runs multivariate tests across email, SMS, and push notifications simultaneously, with statistical significance calculations that update in real time. Klaviyo's native testing is limited to simple A/B splits.

What Does Not Qualify

Most Klaviyo work falls into the "skilled but not R&D" category. That is fine. It does not make the work less valuable to your clients. It just means you cannot claim tax relief on it.

These activities almost never qualify:

  • Setting up standard abandoned cart, welcome, or post-purchase flows. Even if you spend days perfecting the copy and design, that is marketing work, not technological advance.
  • Segmenting audiences based on standard Klaviyo properties. That is configuration, not development.
  • Integrating Klaviyo with Shopify, WooCommerce, or other standard platforms using existing connectors. If the integration is documented and supported, there is no technical uncertainty.
  • Building email templates in Klaviyo's drag-and-drop editor. Even custom HTML templates are design work, not R&D.
  • Any work that a competent Klaviyo developer could complete using publicly available documentation, forums, or standard practices.

The line is not always obvious. If you are unsure, ask yourself this: at the start of the project, did your senior developer say "I do not know if this will work"? If the answer is no, it is probably not R&D.

How the R&D Tax Credit Scheme Works for Agencies

For most agencies structured as limited companies, you claim under the SME R&D tax relief scheme. The enhanced deduction is currently 186% of qualifying expenditure (for accounting periods starting on or after 1 April 2023). That means if you spend £100,000 on qualifying R&D, you can deduct £186,000 from your taxable profits.

If your agency is loss-making, you can surrender those losses for a payable tax credit. The credit rate for loss-making SMEs is 10% of the surrenderable loss (for periods starting on or after 1 April 2023).

For a profitable agency paying 25% corporation tax, every £100,000 of qualifying R&D spend saves you £21,500 in tax (25% of the £86,000 additional deduction). That is real money that can fund more development or improve your bottom line.

If your agency is part of a larger group or has received notifiable grants, you may need to use the RDEC (Research and Development Expenditure Credit) scheme instead. That is less generous but still worthwhile.

What Costs You Can Claim

For a klaviyo custom flow r&d project, the main qualifying costs are:

  • Staff costs: Salaries, employer NI, and pension contributions for the developers, testers, and project managers directly working on the R&D project. You apportion their time based on the hours they spent on qualifying work.
  • Subcontractor costs: If you use external developers, 65% of the payments to them qualify under the SME scheme (unless they are connected to your company).
  • Software licences: If you needed specific tools or cloud infrastructure to run the experiments, those costs can qualify. Klaviyo subscription costs themselves do not qualify unless you used a separate development instance purely for R&D.
  • Consumables: Data storage, API call costs, and any other items consumed in the R&D process.

You cannot claim for general overheads, marketing costs, or the time your directors spend on non-technical work.

Documenting Your Claim Properly

HMRC has become significantly more aggressive in reviewing R&D claims over the last two years. Poor documentation is the fastest way to get your claim rejected or, worse, selected for a full enquiry.

For each qualifying project, you need to document:

  • The technical uncertainty: What exactly did you not know at the start? Be specific. "We did not know whether a real-time scoring algorithm could process 50,000 events per minute without exceeding Klaviyo's API rate limits" is good. "We wanted to improve email performance" is not.
  • The work undertaken: What approaches did you try? What failed? What did you learn from each failure? HMRC wants to see evidence of genuine experimentation, not just a linear development process.
  • The advance sought: What was the technological advance you were trying to achieve? It must be in software engineering, not in marketing or business processes.
  • The time records: Who worked on the project, when, and for how long. Timesheets or project management records are ideal. If you do not have them, start now.

We recommend writing a technical narrative for each project. Keep it to 2-3 pages. Use plain English. A good technical narrative is the single most important document in your claim file.

Common Mistakes Agency Founders Make

I see the same errors repeatedly when reviewing claims from agencies that build Klaviyo flows.

Mistake 1: Claiming for all development work. Just because you built something custom does not mean it is R&D. If you could have achieved the same result by following a tutorial or using an existing library, it does not qualify. Be honest about what was genuinely uncertain.

Mistake 2: Not separating R&D from routine work. Most projects contain a mix of qualifying and non-qualifying activity. A six-week project might have two weeks of genuine R&D and four weeks of standard implementation. Claim only the R&D portion. If you claim the whole project, you invite an enquiry.

Mistake 3: Using retrospective claims without evidence. If you are looking back at work done 18 months ago and have no records of what was uncertain or what you tried, your claim is weak. You can still submit it, but your chances of surviving an HMRC review are low.

Mistake 4: Assuming all Klaviyo custom flows qualify. They do not. The platform is powerful and flexible. Most things you want to build are possible with standard features or documented workarounds. Only claim where you genuinely pushed beyond what the platform supports.

Should You Use an R&D Specialist or Do It Yourself?

You can prepare and submit an R&D claim yourself. The form (CT600L) is straightforward. The hard part is the technical narrative and the cost breakdown.

For a simple claim under £25,000 of qualifying spend, a competent finance person in your agency can probably handle it. For larger claims, or if your project structure is complex, use a specialist. As ICAEW qualified accountants working with agencies, we see the difference a well-prepared claim makes. HMRC enquiries are time-consuming and stressful. Getting the claim right the first time is cheaper than defending a bad one later.

If you are thinking about claiming for the first time, speak to us before you start writing the technical narrative. We can tell you within a 15-minute call whether your Klaviyo work is likely to qualify, and what evidence you need to gather.

Final Thoughts

R&D tax credits are not a reward for doing hard work. They are relief for genuinely advancing technology. If your agency is building custom Klaviyo flows that push the boundaries of what the platform can do, and you can document the technical uncertainty you resolved, you have a legitimate claim.

If you are just building well-crafted automations for clients, keep doing that. It is valuable work. But do not put an R&D claim around it. The risk of an HMRC enquiry is not worth the relatively small relief you might get.

For agencies that do have qualifying projects, the relief is substantial. A £50,000 qualifying project saves around £10,750 in corporation tax for a profitable agency. That is a meaningful amount of cash to reinvest in your team or your own technology stack.

If your contractor mix has changed in the last 12 months, or if you have taken on a project that required genuine technical problem-solving, ask your accountant before year-end. The claim must be made within two years of the end of the accounting period in which the R&D work took place. Miss that window, and the relief is gone permanently.