The verdict in three sentences
Custom practice management software for an accounting firm costs between GBP 55,000 and 130,000 in London in 2026, versus GBP 20 to 45 per fee earner per month for an off-the-shelf suite such as Xero Practice Manager or IRIS. The economic break-even sits around 15 fee earners: below that, subscription wins; above it, custom amortises and you own your tool. The real question isn't the sticker price, it's the 5-year total cost of ownership and how much control you keep over your workflows.
What a custom build actually covers
An accounting firm has specific flows: engagement and job management, time capture per client, time-based billing, a client portal for document collection, and profitability tracking. Here are the 2026 line items for a London build.
| Module | Scope | Range (GBP) |
|---|---|---|
| Jobs & engagements | Engagement letters, deadlines, allocation | 13,000 - 24,000 |
| Time capture | Timesheets per fee earner and job | 9,000 - 16,000 |
| Billing | Time + fixed fee, credit notes, chasing | 11,000 - 22,000 |
| Client portal | Document collection, e-signature, messaging | 13,000 - 30,000 |
| Dashboards | Job profitability, day rate, margin | 9,000 - 22,000 |
| Integration & UAT | API, data migration, testing | 7,000 - 16,000 |
| Total project | Full suite | 55,000 - 130,000 |
Ongoing maintenance and enhancements then run around GBP 850 per month (GBP 10,200 a year). Delivery takes 5 to 9 months depending on scope.
Custom vs suite: the break-even math
Compare a typical firm over 5 years, subscription at GBP 38 per fee earner per month.
| Headcount | Suite / 5 yrs | Custom / 5 yrs* | Verdict |
|---|---|---|---|
| 5 earners | 11,400 | 143,000 | Suite |
| 10 earners | 22,800 | 143,000 | Suite |
| 15 earners | 34,200 | 143,000 | Rough parity |
| 25 earners | 57,000 | 143,000 | Judgement call |
| 40 earners | 91,200 | 143,000 | Custom if strong specifics |
*Custom: GBP 92,000 build + GBP 51,000 maintenance over 5 years. Custom doesn't win on price alone; it wins when your processes are too specific for a standard suite (atypical engagements, complex re-billing, integration with a proprietary tool).
Need a professional website?
Kolonell builds websites that attract clients, optimized for the Sénégalese market. Free quote in 2 minutes.
Mini case study
Sarah, managing partner of a 22-strong firm in London, pays GBP 38 per earner per month, about GBP 10,000 a year on a suite. But she loses hours exporting data to her in-house reporting tool. A custom build at GBP 92,000, plus GBP 850 monthly maintenance, embeds that reporting natively. By recovering 3 % of billable time on GBP 1.5M of fees, she wins back GBP 45,000 a year. Payback lands at roughly 26 months, before counting the quality-of-life gain.
FAQ
What's the minimum viable budget? At least GBP 55,000 for a credible core (jobs, time, billing). Below that you get a prototype, not a production tool for a real firm.
How long to go live? Between 5 and 9 months. A usable first module (MVP) can ship in 3 months if you prioritise time capture and billing.
Is migrating my current data included? Yes, it accounts for GBP 7,000 to 16,000 depending on how clean your exports are. Never underestimate this line.
What if the firm grows? Custom has no per-user cost: going from 22 to 40 earners doesn't change the software bill, only hosting, which is marginal.
Can I keep my suite and bolt on custom? Yes, hybrid is common: the suite handles compliance production, custom handles the client portal and reporting via API.
Let's scope your project. Tell us your headcount, priority modules and target budget, and in one meeting we'll tell you whether custom pays off. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
