The verdict in three sentences
For a practice with 650 client files, a custom client portal costs between EUR 18,000 and 40,000 excluding VAT and pays for itself within 18 to 30 months against a SaaS subscription billed at EUR 4 to 12 per client per month. The real gain is in chasing: aiming for 30% fewer reminders frees almost a full staff day per month. The item not to underestimate is the connector to your accounting software (Xero, QuickBooks, Pennylane or Cegid), between EUR 3,000 and 8,000 depending on sync depth.
Custom or SaaS: what a portal really costs in 2026
The market offers ready-made portals bundled with practice software and dedicated document management tools for accountants. They suit standard practices. Custom development makes sense when the firm wants its own reminder workflows, its own branding, specific year-end questionnaires or multi-entity logic (holding companies, property vehicles, sole traders).
| Option | Upfront cost (excl. VAT) | Recurring cost | For 650 clients over 3 years | Strengths |
|---|---|---|---|---|
| Entry-level SaaS | EUR 0 to 1,500 | EUR 4 per client per month | ~EUR 95,000 | Live in 2 weeks |
| Premium SaaS with DMS | EUR 2,000 to 5,000 | EUR 8 to 12 per client per month | EUR 190,000 to 285,000 | E-signature, OCR, workflows |
| Simple custom portal | EUR 18,000 to 25,000 | EUR 350 to 600 per month (hosting, maintenance) | EUR 31,000 to 47,000 | Own reminders and brand |
| Advanced custom portal | EUR 30,000 to 40,000 | EUR 600 to 1,000 per month | EUR 52,000 to 76,000 | Questionnaires, multi-entity, dashboards |
| Accounting software connector | EUR 3,000 to 8,000 | Included in maintenance | EUR 3,000 to 8,000 | Documents filed with no re-keying |
These amounts are 2026 ballpark figures for development by a specialist agency. The 3-year SaaS cost quickly exceeds the custom option once the practice passes 400 to 500 clients.
The features that cut reminders
A useful portal is not just an upload box. It must turn document collection into a guided process, with deadlines visible to the client and alerts for the accountant.
| Feature | Development effort | Expected impact | Priority |
|---|---|---|---|
| Drag-and-drop and mobile photo upload | 4 to 6 days | No more documents sent by email | Essential |
| Expected documents list per client per month | 5 to 8 days | 15 to 20% fewer reminders | Essential |
| Automatic email and SMS reminders | 3 to 5 days | 10 to 15% fewer manual reminders | Essential |
| OCR and invoice pre-filing | 6 to 10 days | 20 to 30% of data entry time saved | Recommended |
| Year-end questionnaire | 4 to 6 days | Accounts started 2 weeks earlier | Recommended |
| Secure messaging per client | 4 to 7 days | No more scattered email threads | Recommended |
| Certified health-data or sovereign hosting | 20 to 40% hosting premium | Reassures healthcare clients | Optional |
UK GDPR and EU GDPR require a record of processing, defined retention periods and appropriate hosting. Professional bodies also expect access logs, which should be in the specification from day one.
Mini case study
Emma, partner at a 12-person accounting practice in London, manages 650 clients. Her team spends about 3 days a month, or 21 hours, chasing clients by phone and email. At a loaded cost of EUR 45 an hour, that is EUR 945 a month, or EUR 11,340 a year.
She chooses a custom portal at EUR 28,000 plus a connector at EUR 5,000, so EUR 33,000, and EUR 500 a month for maintenance. Target: 30% fewer reminders, worth EUR 3,400 a year, plus about EUR 9,000 of data entry avoided thanks to OCR and automatic filing. Estimated annual gain: EUR 12,400, minus EUR 6,000 of maintenance, so EUR 6,400 net. Against a premium SaaS at EUR 8 per client (EUR 62,400 a year), the custom portal pays back in under 8 months.
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FAQ
How long does it take to deliver an accounting firm client portal?
Allow 10 to 16 weeks for a complete version: 2 weeks of scoping, 8 to 12 weeks of development and 2 weeks of acceptance testing with a panel of 20 to 30 pilot clients.
Can the portal connect to two accounting packages at once?
Yes, if the practice uses different tools for different engagements. Budget EUR 6,000 to 8,000 for connectors, since each API has its own authentication and filing logic.
Will clients actually use the portal?
Practices that support the launch with a video tutorial and a personal reminder reach 60 to 75% adoption within 6 months. The mobile app with receipt photo upload remains the main lever with small businesses.
Who owns the code and the data?
In a custom development contract, the practice should obtain assignment of the code rights and remain sole data controller. Data is hosted in the UK or the EU, with exit provisions written into the contract.
Should we plan a maintenance budget?
Yes, about 15 to 20% of the initial cost per year, so EUR 4,200 to 6,000 for a EUR 28,000 portal. This covers security updates, changes to accounting APIs and small improvements.
Let's scope your project. Tell us your number of clients, your accounting software and your current reminder process, and we will price a portal between EUR 18,000 and 40,000 with a 10 to 16 week schedule. 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.
