Celebrating a Five Year Milestone

Five years ago, I started Onside Accounting with a simple belief: business owners deserved better from their accountants.

After nearly two decades in the profession, I had watched service levels steadily deteriorate across much of the industry. Clients were experiencing slow response times, high staff turnover, limited access to senior people, and an increasing sense that they were just another number on a spreadsheet.

At the same time, many larger firms were becoming increasingly focused on margins and efficiency. Private equity investment had accelerated consolidation across the sector, partner-led relationships were becoming harder to find, and fee increases of 30-50% were becoming increasingly common. Yet despite rising fees, many clients felt they were receiving less support than ever before.

I Believed There Was a Better Way

What if an outsourced accounting provider acted as a genuine extension of your team rather than a distant external adviser? What if your accountant didn’t just have deep sector expertise, but was available when you needed them, joined your Slack channels, responded on WhatsApp, understood your business inside out and supported you through every stage of growth?

That Was the Idea Behind Onside

The timing felt right personally too. During the Covid period, I discovered something that has remained true ever since - I loved working remotely. After spending most of my career in senior leadership roles, I felt ready to build something of my own. I made the decision that I would never return to a traditional office environment and instead build a business designed around flexibility, trust and outcomes.

Five years later, I still feel exactly the same.

Image: From left to right: Stefanie Porter; Molly Jenkins; Martin Brennan; Rachel De Cesaro, Futurecity; Alisha Patel

Building a Different Type of Accounting Firm

From day one, our mission was to support ambitious founders through every stage of their journey.

Many traditional accounting firms struggle when clients grow quickly. A business that moves from Seed to Series A, then Series B and beyond, requires a finance partner willing to invest ahead of demand and scale alongside them.

Our philosophy has always been to build capacity before our clients need it. We want founders to know that when opportunities arise, funding lands, international expansion begins or headcount doubles, we already have the people and expertise in place to support them.

That focus naturally led us towards venture-backed technology companies - ambitious businesses operating at pace and building for scale.

Today, we have a team of around 50 talented people located across the UK, all connected by a shared belief that great work doesn't require a traditional office.

Growth has always been one of our defining values. Not just growth for our clients, but growth for our people. We have built a culture around learning, curiosity and progression. Alongside Growth, our values of Care, Positivity, Togetherness and Curiosity continue to shape how we work every day.

Image: Ryan Snape, Managing Director, Onside Tax (middle) with Linda Lipkova, Head of Accounting (left) and Molly Jenkins, Head of Finance and Operations (right)

Growing Through Trust

If I had to attribute our success to one thing, it would be this: look after your existing clients.

More than 95% of our clients have come to us through referrals. Existing clients recommending us to fellow founders. Venture capital investors introducing portfolio companies. Lawyers, consultants and partners trusting us with businesses they care about.

There is no marketing strategy more powerful than doing great work consistently.

That trust has allowed us to grow every year since launch, achieving more than 50% growth year-on-year while remaining focused on service quality and client experience.

We've invested heavily in people throughout that journey. In many cases, we've hired ahead of immediate demand because we know our clients' growth plans require us to be ready before they need us.

I'm particularly proud that many of our leaders today were among our earliest hires. They have helped shape the culture, standards and environment that make Onside what it is.

As our clients have grown, so have we. What started as accounting support has naturally expanded into broader finance, tax and advisory services. Today, we support businesses with everything from day-to-day finance operations through to CFO services, international expansion and strategic growth planning.

This summer, we'll also be launching expanded US service capabilities - another step in helping our clients scale globally.

Milestones We're Proud Of

Over the last five years, there have been many moments worth celebrating.

We've grown from a one-person startup into a national team of around 50 people.

We've supported hundreds of ambitious businesses and worked alongside many of the UK's leading venture capital funds and startup ecosystems.

We've maintained exceptionally strong client and employee satisfaction scores year after year.

We've received industry recognition through multiple awards, including what was undoubtedly one of our proudest achievements - being named Medium to Large Firm of the Year for Client Service at the Accounting Excellence Awards, widely regarded as the most prestigious awards in the UK accounting profession.

Thank You

But beyond the awards and growth figures, what matters most is the impact we've had on the businesses and people we support every day.

To every client who trusted us, particularly in those early years, thank you.

To every member of our team, thank you for your hard work, loyalty, professionalism and commitment. It is genuinely a privilege to work alongside people who care so deeply about helping clients succeed.

To the venture capital firms, lawyers, consultants and partners who continue to recommend us, thank you for the trust you place in our team.

I've always tried to be authentic and to do exactly what I say I will do. The only reason I've had the opportunity to build a business around those principles is because so many people have trusted us along the way.

For that, I am incredibly grateful.

Looking Ahead

When I started Onside five years ago, I assumed the first five years would be the most exciting chapter.

I was wrong! The next five years look even more exciting.

Our profession is approaching a period of significant change driven by advances in artificial intelligence and technology. While many view AI primarily through the lens of efficiency and cost reduction, that's not how we see it.

For us, AI is an opportunity to create a better experience for clients and a better experience for our people.

It allows us to remove friction, improve responsiveness, provide deeper insights and free talented professionals to focus on the work that creates the most value.

Through our partnership with Multiplier and the world-class team they are building, we believe we are exceptionally well positioned to lead this change rather than follow it.

Our ambition remains the same as it was five years ago: to become the leading finance partner for ambitious founders.

We're just getting started!

Martin Brennan, Founder and CEO, Onside Accounting and Onside Tax