Thomas Shelley has seen the inside of a tax preparer’s inbox. As the former Head of Product at tax software maker Keeper, he knows the workflow: a flood of client documents, from scribbled charity receipts to complex multi-state K-1s, all needing manual data entry into systems like UltraTax or ProConnect [promptloop.com, 2026]. It’s a bottleneck of human error and billable hours. His new company, Magnetic, is betting that bottleneck is now a software problem. The Y Combinator-backed startup is building an AI agent designed to scan that chaotic document pile and auto-fill the corresponding fields in legacy tax software, claiming over 90% field-level accuracy [Y Combinator, June 2025].
The wedge into a $50 billion workflow
The bet is straightforward. Magnetic sells to CPA firms as a SaaS layer that sits atop the tax preparation software they already use. The product’s stated job is to reason over complex documents, reference tax code, and handle calculations like state tax-exempt interest allocation, then push the results directly into the preparer’s workflow [Y Combinator, June 2025]. The value proposition is time and accuracy, not displacement. For a profession facing perennial staffing shortages and margin pressure, automating the most tedious part of the job is a compelling wedge. The total addressable market is the roughly $50 billion spent annually on tax preparation services in the US, a figure that underscores the scale of the manual labor Magnetic is targeting.
A team built on prior scale
The founders bring relevant, scaled experience. Shelley and co-founder Patrick Fay have previously built software used by millions of people and processed tens of thousands of tax returns, according to the company [magnetictax.com/about, 2026]. Shelley’s background specifically includes developing tax engine automation and OCR form-scanning tools at Keeper, a YC company itself [promptloop.com, 2026]. This isn’t a team attacking the problem from first principles; it’s one applying prior lessons in tax software and data extraction to a more focused, AI-native automation layer. Their early backing from Y Combinator’s Summer 2025 batch, led by partner Jared Friedman, provides the standard runway (an estimated $500,000) to prove the accuracy claims and find initial design partners [Y Combinator, June 2025].
Where the accuracy claim meets reality
The entire thesis hinges on that 90%+ accuracy figure. In tax preparation, a 10% error rate is not a minor bug; it’s a potential audit trigger and a professional liability. Magnetic will need to demonstrate that its AI’s confidence scores are reliable and that its errors are easily caught and corrected by a human reviewer in the workflow. The competitive landscape, while nascent, includes other startups like Black Ore and Filed aiming at similar automation. Magnetic’s differentiation appears to rest on a deep focus on the CPA firm’s existing toolchain, avoiding a rip-and-replace model.
The primary risks are not conceptual but executional:
- Integration depth. smooth, reliable integration with closed, monolithic systems like UltraTax or Drake is a non-trivial technical hurdle.
- Data complexity. Handwritten notes, scanned PDFs, and spreadsheet schedules present a wildly variable input dataset that challenges even advanced OCR and LLM reasoning.
- Sales motion. Convincing traditionally conservative accounting firms to trust an AI with sensitive client data requires a proven track record Magnetic has yet to build.
For now, Magnetic is in the build-and-prove phase typical of a YC seed company. The next twelve months will be about converting that undisclosed Y Combinator capital into a handful of lighthouse customer deployments that can validate the accuracy claims in production. The question for Shelley and Fay is whether they can move from a compelling demo to a trusted, billable component of a CPA’s April crunch. If they can, the legacy tax software stack might just get its first AI-native layer.
Sources
- [Y Combinator, June 2025] Magnetic (Y Combinator S25) | https://www.ycombinator.com/companies/magnetic
- [promptloop.com, 2026] What Does Magnetic Do? - Company Overview | Directory | https://www.promptloop.com/directory/what-does-magnetictax-com-do
- [magnetictax.com/about, 2026] Magnetic - AI Tax Preparation | https://www.magnetictax.com/about
- [Crunchbase, 2026] Magnetic - Crunchbase Company Profile & Funding | https://www.crunchbase.com/organization/magnetic-4d00