Secure client portal cost for an accounting firm in London in 2026

The verdict in three sentences

A custom secure client portal for an accounting firm in London is budgeted between EUR 18,000 and EUR 40,000 in 2026, document vault and e-signature included. Plan for 12 to 16 weeks from design to production, with SSO and MFA mandatory to protect tax filings. Over three years, the custom build becomes cheaper than SaaS billed at EUR 12 to 25 per user per month as soon as you pass roughly thirty active staff.

What a custom client portal costs in 2026

The price depends on functional scope and the security level required by accounting data. Here is a 2026 order-of-magnitude breakdown for a firm of 15 to 40 staff in London.

The core alone varies widely: a Starter portal at EUR 18,000 covers document upload, messaging and notifications, while a Premium version at EUR 40,000 adds approval workflows, multi-company spaces and custom tax dashboards.

Custom build vs SaaS: the 3-year calculation

Market SaaS portals bill per user. Custom is an upfront investment that amortizes. Comparison for 35 users over 36 months.

At 35 users the SaaS stays cheaper in cash. But from 55 users or if the firm bills the portal to its clients, custom pulls ahead while keeping data control and a unique brand.

Mini case study

Claire runs a 32-staff accounting practice in central London. Her teams still exchange around 400 documents a month by email, a GDPR risk and an estimated 18 hours/month of filing. She invests EUR 26,000 in a custom portal with vault and signature.

At a loaded hourly cost of EUR 45, the 18 hours saved represent EUR 810/month, or EUR 9,720/year. The portal pays back in about 32 months, before counting the reduced data-leak risk and the e-signature that speeds up filing delivery.

FAQ

How long to launch a secure client portal?

Plan 12 to 16 weeks in 2026: 3 weeks of scoping, 8 to 10 of development, the rest for testing and training. A Starter scope without an accounting connector can drop to 10 weeks.

Is e-signature really necessary?

For an accounting firm, yes: it secures approval of filings and engagement letters. The eIDAS advanced module costs around EUR 4,000 and removes paper back-and-forth.

Are the EUR 12-25/user/month SaaS worth it?

They are economical below 30 users and for a standard need. Beyond that, or if you want customization and data ownership, custom becomes more cost-effective over 3 years.

How do you guarantee accounting data security?

SSO, MFA, encryption at rest and in transit, EU hosting and access logging. This security core costs around EUR 3,500 and is non-negotiable for tax data.

Can we bill the portal to our clients?

Yes, many firms include portal access in their package or bill it at EUR 5-10/month per client, which accelerates build payback.

Let's scope your project. Tell us your file volume, your accounting connectors and your target budget (EUR 18,000 to 40,000): we scope the security core first. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.