The verdict in three sentences
A vertical solution remains unbeatable for pure accounting production: tax filings, review and payroll are already standardised and updated with every finance act. Custom software is only justified where the vendor holds you back: a specific client portal, an engagement workflow, a capacity dashboard, integrations the licence does not cover. The right 2026 call is almost always hybrid: keep the vertical production engine and build the client-relationship and steering layer custom, for 60,000 to 140,000 EUR.
What it really costs in 2026
The figures below are 2026 orders of magnitude for a Dublin firm of 15 to 40 staff.
| Item | Vertical solution | Custom module |
|---|---|---|
| Licence / user / month | 40 to 90 EUR | 0 (owned) |
| Entry cost (setup) | 3,000 to 12,000 EUR | 60,000 to 140,000 EUR |
| Legal updates | Included | On you (maintenance) |
| Deep customisation | Limited | Total |
| Annual maintenance | Partly included | 15 to 20 % of build |
| Time to go live | 4 to 8 weeks | 4 to 7 months |
5-year TCO: the real match
Let's compare for a 25-staff firm, assuming 65 EUR/user/month for the vertical and a 100,000 EUR custom build.
| Element | Vertical (5 yrs) | Custom (5 yrs) |
|---|---|---|
| 25 user licences | 97,500 EUR | 0 |
| Initial setup | 8,000 EUR | 100,000 EUR |
| Maintenance / evolutions | 10,000 EUR | 85,000 EUR |
| Hosting | Included | 9,000 EUR |
| Total 5-year TCO | 115,500 EUR | 194,000 EUR |
| Capitalised asset | No | Yes (owned code) |
The vertical is cheaper for production. Custom only pays off when it replaces a high-value task (billing, collection, steering) that drains billable hours every week.
Functional coverage and vendor lock-in
| Criterion | Vertical | Custom |
|---|---|---|
| Up-to-date tax filings | Excellent | To maintain |
| Personalised client portal | Weak | Excellent |
| Engagement workflow | Standard | Bespoke |
| Data export / reversibility | Often limited | Total |
| Vendor lock-in | Strong | None |
| Hours saved / staff / month | 2 to 4 h | 5 to 9 h |
Mini case study
Mark, a partner in a 25-staff Dublin firm, keeps his vertical tool for production but builds a custom client portal (document collection, signature, engagement tracking) for 92,000 EUR. Each team member saves 6 hours a month of chasing and re-keying, i.e. 25 x 6 = 150 hours/month. Valued at 55 EUR of billable time, that is 8,250 EUR of capacity returned each month, or 99,000 EUR a year: the build pays for itself in under 12 months, before any client-satisfaction gain.
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FAQ
Should we drop our vertical tool for custom software?
Rarely. Standardised production (filings, review, payroll) is the vendors' strength and would cost a fortune to rebuild. Keep the vertical and build custom only where it constrains you: portal, workflow, steering.
What is the minimum budget for a useful custom module?
Budget 60,000 EUR for a solid first module (client portal + collection + tracking). Below 30,000 EUR you stay at prototype level or a targeted automation.
How long to deliver?
From 4 to 7 months depending on scope, with a first usable version in 8 to 10 weeks if the MVP is well framed.
How do we avoid a new dependency?
Owned code delivered, documentation, hosting on your own or a neutral cloud, and a fixed annual maintenance fee of 15 to 20 % of the build. You stay the owner, free to switch supplier.
Is custom software GDPR-compliant?
Yes, and it is even an advantage: EU hosting, encryption, logging and fine-grained access control are built in from the start, without vendor-imposed compromise.
Let's scope your project. Tell us your current stack (vertical tool, headcount, modules to build) and your indicative budget. 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.
