Accounting Firm Client Portal Build Cost in London (2026)

The verdict in three sentences

For a London practice with 300 to 1,200 clients, a custom client portal costs between 25,000 and 60,000 GBP (excluding VAT) and ships in 10 to 16 weeks. It beats an off-the-shelf portal billed at 3 to 12 GBP per client per month once the practice passes roughly 500 clients or needs a deep link to its production software. Payback typically lands between 14 and 20 months, driven mostly by the end of manual document chasing.

What a client portal really costs in 2026

Price depends less on the number of screens than on integrations: practice management and production software, document management, e-signature and bank feeds. Here are the ranges seen in London (2026 estimates, excluding VAT).

Add maintenance (usually 12 to 18% of the build per year) and hosting, around 100 to 300 GBP per month depending on storage volume.

Custom or off-the-shelf: the numbers side by side

Off-the-shelf portals from accounting software vendors or specialist platforms start fast, but their cost climbs with client count and they impose their own client journey.

Below 250 clients, off-the-shelf is often the right call. Above 500, custom pays back faster, especially for firms selling advisory, payroll or company secretarial work that standard tools handle poorly.

The features that actually save time

Document collection is the first win. A good portal shows each client the exact list of documents expected per engagement, with status and due date, then sends automatic reminders at D-15, D-7 and D-2 before each deadline (VAT, Self Assessment, year-end accounts). Equipped firms usually see manual chasing drop by 50 to 70%.

Next come e-signature for engagement letters and returns (1 to 2 GBP per document), secure sharing of accounts, messaging tied to the client file rather than a staff inbox, and a dashboard showing partners which files are blocked by missing documents.

Mini case study

Claire, partner at a 14-person firm in Islington, manages 820 clients. Her team spends 8 hours a week chasing documents, about 370 hours a year. At a loaded hourly cost of 55 GBP, that chasing costs 20,350 GBP a year. A custom portal quoted at 42,000 GBP, plus 6,300 GBP annual maintenance, cuts chasing by 60%, saving 12,210 GBP a year, plus roughly 11,000 GBP of billing recovered through faster year-end closes. Net annual gain: about 16,900 GBP. Breakeven arrives around month 30 on the build alone, but against 3 years of an off-the-shelf tool at 4 GBP per client per month (about 118,000 GBP), the custom route is cheaper from year two.

FAQ

How long does a custom client portal take to launch?

Allow 10 to 16 weeks from discovery to production. A 3-week pilot with 50 to 100 clients lets you fix the journey before opening it to everyone.

Can the portal connect to our production software?

Yes, in most cases, through the vendor API or scheduled exports. This item costs 5,500 to 16,000 GBP depending on how open the software is.

What UK GDPR obligations apply to an accounting portal?

UK or EU hosting, document encryption, two-factor authentication and an up-to-date record of processing. Budget 1,500 to 3,500 GBP for security and configuration review.

Is e-signature included?

Integration costs 2,000 to 5,500 GBP, then each signed document costs 1 to 2 GBP from the trust provider. For 800 engagement letters a year, that is 800 to 1,600 GBP.

From how many clients does custom make sense?

As a rough 2026 benchmark, from 400 to 500 active clients. Below that, a subscription at 3 to 12 GBP per client per month is usually cheaper over 3 years.

Let's scope your project. Tell us your client count, production software and priority engagements, and we will quote a portal between 25,000 and 60,000 GBP with a 10 to 16 week plan. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.