The verdict in three sentences
In 2026, custom practice management software for a London accounting firm costs between 40,000 and 100,000 EUR, delivered in 4 to 7 months. A vertical licence (Cegid, IRIS, Xero Practice Manager) is cheaper to start — 30 to 60 EUR/staff/month — but locks you into a fixed scope. Custom pays off as soon as you want to automate tax-deadline tracking, time spent and billing in a single flow, with a measured gain of 5 to 8 hours/week/staff member.
What custom costs in 2026
The budget depends on the number of modules and the volume of data to migrate. Here is a 2026 order of magnitude for a firm of 8 to 20 staff in London.
| Module | Scope | 2026 cost (EUR) | Timeline |
|---|---|---|---|
| Tax deadline tracking | VAT, corporation tax, returns, alerts | 9,000 - 18,000 | 4-6 wk |
| Time entry | Timesheet per file/engagement | 7,000 - 14,000 | 3-5 wk |
| Client billing | Quotes, fees, reminders | 8,000 - 16,000 | 4-6 wk |
| Secure client portal | Document upload, DMS | 7,000 - 15,000 | 4-6 wk |
| Partner dashboard | Profitability per file | 6,000 - 12,000 | 3-4 wk |
| Data migration | Legacy tool import | 4,000 - 12,000 | 2-4 wk |
| Project total | Full base | 41,000 - 87,000 | 4-7 months |
Add annual maintenance of 15 to 20 % of the development cost, i.e. 6,000 to 17,000 EUR/year, covering fixes, upgrades and regulatory changes.
Custom vs vertical licence: the real math
The licence looks unbeatable in year one. Over four years the gap narrows — and custom removes the per-seat costs that balloon as the firm grows.
| Item | Vertical licence | Custom software |
|---|---|---|
| Upfront cost | 0 - 3,000 EUR (setup) | 41,000 - 87,000 EUR |
| Monthly cost (12 staff) | 360 - 720 EUR/month | 0 (hosting 60-150 EUR) |
| 4-year cost | 17,000 - 37,000 EUR | 55,000 - 105,000 EUR |
| Code ownership | No | Yes |
| Process fit | Limited | Total |
| Cost per added staff member | +30-60 EUR/month | 0 |
Mini case study
Claire, partner in a 14-staff accounting firm in London, loses considerable time juggling her production tool, a deadline spreadsheet and a billing app. She invests 62,000 EUR in unified custom software.
Estimated gain: 6 hours/week/staff member recovered on entry and reminders. At a loaded cost of 45 EUR/h, that is 14 x 6 x 45 = 3,780 EUR/week, roughly 170,000 EUR/year of productive capacity. Even valuing only 30 % of that gain as billable revenue, the return on investment is reached in under 15 months, maintenance included.
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FAQ
How much exactly does custom software cost for my firm?
Expect 40,000 to 100,000 EUR in 2026 depending on the number of modules. A deadlines + time + billing base starts around 40,000 EUR.
How long before go-live?
Between 4 and 7 months for a firm of 8 to 20 staff, including one month of data migration and training.
Is it really cheaper than a Cegid or Xero licence?
Not in year one. Over 4 years the gap narrows sharply and custom removes the per-seat cost — decisive beyond 15 staff.
Can my historical data be migrated?
Yes. Migration from your current tool costs 4,000 to 12,000 EUR depending on volume and data-cleaning needs.
Who handles regulatory changes (VAT, returns)?
They are covered by the annual maintenance (15-20 %), which includes regulatory and corrective updates.
Let's scope your project. Tell us about your firm (staff count, priority modules, indicative budget, target timeline) and we will price your custom practice management software. 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.
