What Onside Accounting does

Onside Accounting Limited is a London-headquartered, UK-registered private limited company founded in 2021 by Martin Brennan FCCA, operating as a Chartered Certified Accountancy and business advisory firm. The firm serves approximately 200 VC-backed technology startups and scale-ups from pre-seed through Series C, providing a three-person dedicated finance team led by a Chartered Accountant, plus on-demand access to specialist tax advisers and an in-house fractional CFO. Core service lines include bookkeeping, management reporting, statutory accounts, VAT, payroll, corporation tax compliance (via the Onside Tax sub-brand), R&D tax credits, EIS/SEIS and EMI share scheme advisory, transfer pricing, personal tax, and cross-border UK/US support. The firm operates as part of the Multiplier group, a San Francisco-based portfolio of professional services businesses backed by Ribbit Capital and Lightspeed Venture Partners.

Onside is an Xero Platinum Partner and works exclusively with Xero as its accountancy platform, supported by an integrated partner stack including Apron for payments, BrightPay Cloud for payroll, and Rippling and Remote for HR and global employment. The firm is remote-first with bi-annual company meet-ups and is structured around a referral-driven, consultative sales model embedded in the UK VC and angel investor ecosystem; founder Martin Brennan is an active angel investor and sits on the ACCA Global Council and the Apron Advisory Board. Revenue is generated primarily through recurring monthly subscriptions for compliance and fractional CFO services, supplemented by project-based professional services for tax advisory, R&D claims, and cross-border structuring. Pricing is quote-based and not publicly disclosed. The firm was recognised in 2025 with the Accounting Excellence Awards 'New Firm of the Year' and 'Silver Mid-Tier Firm' honours.

Name

Onside Accounting

Legal name

Onside Accounting Limited

Website

https://onsideaccounting.com

Company type

Private

Founded year

2021

Operating status

Operating

Headcount range

11–50 employees

Short description

Onside Accounting is a London-based Chartered Accountancy firm founded in 2021 that serves approximately 200 VC-backed UK technology startups and scale-ups from pre-seed through Series C, delivering dedicated finance teams, tax advisory, R&D credits, fractional CFO, and cross-border UK/US services as part of the Multiplier group.

Ownership category

akta.pro rank

Product category

Startup Accounting and Tax Advisory

NAICS

Offices of Certified Public Accountants (541211), Other Accounting Services (541219)

akta.pro primary industry

Accounting & Bookkeeping Services (BPAHABAC)

akta.pro secondary industries

Transaction Tax Structuring & Deal Advisory (BPAHAOAJ), Financial Reporting & Technical Accounting Advisory (GAAP/IFRS) (BPAHABAF)

Keywords

• Accounting and tax compliance
• R&D tax credits
• Fractional CFO services
• Tax advisory
• Startup accounting

Headquarters

HQ city

London

HQ country

United Kingdom

HQ region

Europe

Offices1 record

Markets served

GTM type

B2B

Offering type

Services

Cost components

Personnel, Operations, Marketing or Sales, Technology or R&D, Infrastructure

Revenue model

1. Accounting & Tax Compliance Services: Ongoing statutory, operational, and compliance services including bookkeeping, management reporting, year-end accounts, VAT filings, payroll processing, and corporation tax returns. Delivered through dedicated three-person finance teams led by Chartered Accountants.
2. Tax Advisory Services: Specialist tax advisory covering R&D Tax Credits, EIS/SEIS investment schemes, EMI share schemes, international and transfer pricing, business restructuring, and personal tax advisory. Delivered by Chartered Tax Advisers.
3. Fractional CFO / Finance Director Services: High-level financial expertise at a fraction of the cost of a full-time CFO, providing financial modelling, process improvement, stakeholder management, board reporting, and strategic finance support on a flexible, scalable basis.
4. US Services: Cross-border tax, bookkeeping, and finance support for UK startups expanding into the US, including US entity structuring, federal and state tax returns, EIN applications, Delaware annual reports, and PFIC/CFC compliance.

Pricing tiers

Go-to-market motion2 records

Distribution channels2 records

Marketing channels6 records

Core offering

Onside Accounting provides a dedicated three-person finance team led by Chartered Accountants for each client, delivering day-to-day bookkeeping, management reporting, payroll, VAT filings, statutory accounts, and corporation tax compliance. The firm layers specialist advisory on top, including R&D tax credits, EIS/SEIS and EMI share scheme support, fractional CFO services, cross-border US tax and accounting, and transfer pricing advisory, exclusively serving VC-backed technology startups and scale-ups from pre-seed through Series C.

Product overview

Onside Accounting operates as a unified finance partner for tech startups, combining core accounting and tax compliance with specialist advisory modules. The offering is structured around a dedicated three-person finance team (led by Chartered Accountants) supported by specialist add-ons: Onside Tax (R&D tax credits, EIS/SEIS, EMI schemes), Fractional CFO Services, US Services, and Transfer Pricing Advisory. All services are delivered through a single integrated team using Xero as the primary accounting platform, with payroll processed via BrightPay Cloud and payments via Apron.

Differentiator

Problem solved

Functional benefit

Brands

• Onside Tax: Tax advisory services including R&D tax relief, EIS/SEIS investment schemes, EMI share option schemes, business tax advisory, and personal tax advisory services for UK businesses and individuals.

Products and services

• Core Accounting & Tax Compliance Ongoing statutory, operational, and compliance services including bookkeeping, monthly management reporting, year-end accounts, VAT returns, payroll processing, corporation tax returns, and company secretarial tasks. Delivered through a dedicated three-person finance team led by Chartered Accountants, and aimed at UK VC-backed tech startups and scale-ups from pre-seed through Series C.
• Onside Tax

Quantifiable outcome

• R&D tax relief of up to 27% of qualifying expenditure returned from HMRC
• +2 more outcomes

Named customers10 records

Segments3 records

Ideal customer profiles3 records

Technology focussed No

API detail

Has API

No

API docs

API detail

Core technology

AI maturity

App detail

Integration4 records

Feature1 record

Partnerships

Six partnerships are on record, tiered core and minor.

• MultipliercoreStrategic or Co-development PartnerOnside recently entered a strategic partnership with Multiplier, a San Francisco-based technology company backed by Ribbit Capital and Lightspeed Venture Partners, to accelerate the development of technology that improves client and staff experience. Onside is part of the Multiplier group, a fast-growing portfolio of professional services businesses.
• AproncoreTechnology or IntegrationApron is a Series B fintech where Martin Brennan sits on the Advisory Board. Apron is featured as a partner in the ecosystem, with Onside overseeing payroll payment files into Apron for certain clients. Apron powers payment workflows for the firm's client finance operations.
• XerocoreTechnology or IntegrationXero Platinum Partner. Onside works exclusively with Xero as their chosen accountancy system provider. This exclusive partnership enables deep expertise in Xero's ecosystem, with Onside recognised as a Platinum-level partner demonstrating highest competency and client delivery standards.
• Operations NationminorGTM or Marketing PartnerOperations Nation is a partner and referral source. Ausrinė Kersanskaitė, Co-Founder of Operations Nation & Head of Operations at Reframe Technologies, is a client and advocate for Onside, demonstrating the referral relationship.
• Legal EdgeminorChannel Partner/ Reseller/ DistributorLegal Edge is featured as a partner, likely providing legal services to shared startup clients requiring legal support alongside accounting and tax services.
• Wilson Sonsini Goodrich & Rosati (WSGR)minorChannel Partner/ Reseller/ DistributorWilson Sonsini, a leading technology and life sciences law firm, is featured as a partner, likely serving as a referral source for startup clients needing legal counsel for fundraising, M&A, and corporate matters alongside Onside's financial services.

Scale indicators4 records

Recent moves7 records

Expansion highlights5 records

Direct peers

• Pilot.com: US-based tech-enabled bookkeeping, accounting, and CFO services firm purpose-built for startups and venture-backed companies. Closest US analogue to Onside's bundled compliance-plus-strategic-finance model.
• Kruze Consulting: US-based chartered accounting firm specialising in VC-backed startups, with R&D tax credits, fractional CFO, and bookkeeping services. Directly comparable mission, target market, and service mix.
• Crisp Accounting: UK-based chartered accountancy firm exclusively focused on tech startups and scale-ups, with similar R&D tax credit, EIS/SEIS, and fractional CFO offerings. Closest direct competitor in the VC-backed startup niche.
• Ember Accountancy: UK chartered accountants focused on tech startups, scale-ups, and SMEs. Similar Xero-native, cloud-first approach and target market of VC-backed founders.
• 10x Accounting: UK-based accountancy firm specialising in startups and scale-ups across the full lifecycle. Highly comparable service catalogue and GTM motion targeting tech founders.

Broad incumbents

• Cooper Parry: UK Top-30 chartered accountancy firm with a defined tech and VC-backed startup proposition. Comparable service breadth (compliance, advisory, fractional CFO) but serves a broader client base.
• BDO Private Business / BDO Private Equity: Large international accounting network with a dedicated private-business and private-equity startup practice. Competes for the same VC-backed startup clients but as part of a much broader portfolio of services.
• KPMG Private Enterprise: Big-4 practice focused on founder-led and VC-backed growth businesses. Competes in the upper end of Onside's market (Series B+ clients) with much broader capabilities.

Others

• Hintze Law (cross-border tax and structuring): Specialist international tax and structuring advisory firm serving UK and US high-growth tech companies. Adjacent rather than competing, with overlap in transfer pricing and cross-border tax work.

Emerging players

• Auxo.co: Tech-driven bookkeeping and accounting firm for high-growth US startups. Comparable in bundling software-led accounting with finance support, less established in the UK market.

Market position

Strengths5 records

Weaknesses5 records

Competitive moat5 records

Key risks6 records

Key highlights7 records

Customer concentration

• LinkedInlinkedin.com/company/onside-accounting

Compliance1 record

Revenue estimate

Valuation estimate

Number of profiles

Profiles9 records

Subsidiaries1 record

Funding overview

Funding rounds

Investors

Funding detail is available on the Subscription and Enterprise plan.Contact sales →

M&A

Investments

M&A and investment is available on the Subscription and Enterprise plan.Contact sales →

Frequently asked questions about Onside Accounting