Why SumTax exists
Self Assessment shouldn't mean hours of forms or a bill in the hundreds. Most people simply need their tax worked out correctly and filed properly.
About Us
Financial expertise meets intelligent technology.
SumTax brings together expertise in finance, accounting and technology to make UK Self Assessment simpler and more affordable. Our secure agentic platform handles much of the preparation, while our finance experts keep the rules right.
Mark Devine
Founder & CEO
Meet our founder
A CFO's view of what tax should feel like.
Mark is an experienced CFO and COO with decades of experience running large companies. Mark also holds a first class BA and MA in Economics from Oxford University and was awarded the Dean's Award on his MBA at Oxford for the highest academic performance.
Mark has championed agentic transformation in his industry roles and has seen early how agentic technology can transform finance work. Mark founded SumTax to bring that to everyday UK taxpayers: fast, affordable returns, with professional validation.
Today Mark leads SumTax's team of accounting professionals and technology experts.
CFO & COO
Decades running large companies
First class BA & MA
Economics, University of Oxford
MBA, Oxford
Dean's Award for highest academic performance
Agentic transformation
Championed in industry roles
What we stand for
Built by finance people, powered by technology.
Our finance expertise
SumTax is shaped by people who have worked in finance and accounting, and understand where real returns go wrong.
Our technology expertise
Our proprietary agentic platform gathers, organises and checks information, doing in milliseconds what used to take hours.
Responsible agentic automation
Technology prepares and explains. A deterministic, versioned tax engine does the maths. Anything requiring judgement goes to a person.
You stay in control
Every return is validated against HMRC's rules, then you review and submit it yourself.
Security and customer trust
Private document storage, restricted access, consent-based HMRC connections and nothing filed without your approval.
Meet the team
The people behind SumTax.
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Tax specialist
Name and credentials to follow.
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Technology lead
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Client success
Name and credentials to follow.
Tax sorted. Without the usual bill.
Calculate for free. Validate and submit yourself from £79.