The verdict in three sentences
For a 20-person statutory audit firm in London managing 250 engagements, a custom engagement management system costs between 30,000 and 52,000 GBP in 2026, delivered in 4 months. An off-the-shelf practice management package at about 75 GBP per user per month comes to 18,000 GBP a year for 20 seats, which matches the cost of a custom build within two to three years. Custom software makes sense when your reappointment alerts, fee tracking and partner rotation rules do not fit the standard screens.
What the software must cover in an audit firm
Audit appointments are renewed every year, and partner rotation rules apply to public interest entities. Across 250 clients, roughly 40 engagements change scope or team every year, and a missed engagement letter update is usually discovered when the planning meeting is already booked. The useful scope breaks down into modules that can be priced separately.
| Module | Key function | Share of budget (2026 estimate) |
|---|---|---|
| Client and engagement register | Entities, year ends, appointment date, rotation date | 15 % |
| Engagement letters | ISA 210 templates, generation, e-signature, archiving | 20 % |
| Deadline alerts | Reappointment at D-180, D-90, D-30, partner rotation | 10 % |
| Budgets and fees | Hour budget per engagement, rate card, actual vs budget | 20 % |
| Time recording | Timesheets per engagement and per phase | 15 % |
| Billing and chasing | Interim bills, final bills, reminders, accounting export | 10 % |
| Partner dashboards | Profitability per client, recovery rate, team workload | 10 % |
The most underestimated item is compliance: traceable client acceptance, independence checks, and retention of signed letters for the regulatory period. An ICAEW or FRC quality review expects these documents to be found in minutes.
Off-the-shelf vs custom: the numbers
Most firms start with a practice management package. It works well as long as your processes match its model. The maths changes when you pay for 20 licences to use 40 % of the features, or when partners still keep a parallel Excel file for deadlines.
| Criterion | Off-the-shelf package | Custom build |
|---|---|---|
| Upfront cost | 1,700 to 4,300 GBP for setup | 30,000 to 52,000 GBP |
| Annual cost (20 users) | 18,000 GBP (75 GBP/month/user) | 3,400 to 6,000 GBP (hosting, maintenance) |
| 5-year total cost | 92,000 to 94,000 GBP | 47,000 to 82,000 GBP |
| Time to go live | 4 to 8 weeks | 4 months |
| Fit with firm rules | Limited to settings | Full |
| Ownership of data and code | Vendor | Firm |
| Main risk | Price rises, imposed features | Weak scoping at the start |
These are 2026 orders of magnitude for the UK market. Over five years, the gap comes mainly from per-user licensing: every new hire increases the package bill, not the custom one.
Detailed budget for a custom project
| Item | Essential version | Full version |
|---|---|---|
| Scoping and partner workshops | 3,000 GBP | 5,200 GBP |
| Engagement register and alerts | 6,000 GBP | 9,500 GBP |
| Engagement letters and e-signature | 6,500 GBP | 10,400 GBP |
| Time, budgets and fees | 7,700 GBP | 13,000 GBP |
| Billing and accounting export | 3,900 GBP | 6,900 GBP |
| Data migration | 1,700 GBP | 3,500 GBP |
| Testing, training, go-live | 1,200 GBP | 3,500 GBP |
| Total | 30,000 GBP | 52,000 GBP |
A typical 4-month plan: 3 weeks of scoping, 10 weeks of development in releases, and 3 weeks of acceptance testing with two partners and one senior manager.
Mini case study
Helen, audit partner at a 20-person firm in London (250 engagements), compares two options. The package costs 18,000 GBP a year. The custom build, mid-range version, costs 41,000 GBP plus 4,800 GBP a year for maintenance and hosting.
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- Over 5 years, package: 18,000 x 5 = 90,000 GBP.
- Over 5 years, custom: 41,000 + 4,800 x 5 = 65,000 GBP.
Then add the time recovered. Managers spent 2 hours a week reconciling recorded time with budgets in Excel. Across 6 managers and 45 weeks, that is 540 hours a year, valued at 60 GBP internal cost, or 32,400 GBP of time returned to chargeable work. This hypothetical scenario shows a payback under 18 months.
FAQ
How much does custom engagement management software cost for an audit firm?
Budget 30,000 to 52,000 GBP for a firm of 15 to 30 people in 2026. The cost depends mostly on the fees module and data migration. Maintenance then runs at 10 to 12 % of the initial cost per year.
How long does it take to go live?
Plan for 4 months for a full scope. It is wise to start outside busy season, for example in May for a September launch.
Can the software handle reappointment alerts and partner rotation?
Yes, it is one of the first modules to build. Alerts go out at D-180, D-90 and D-30, and the rotation rule for public interest entity partners is checked automatically.
Can we migrate our Excel files and old package?
Yes, data migration costs 1,700 to 3,500 GBP depending on file quality. Firms usually migrate 5 years of time and fee history.
Where is the data hosted?
The software can be hosted with a certified provider in the UK or the EU, for about 70 to 170 GBP a month. Daily backups and access logs are included.
Let's scope your project. Tell us your number of engagements, users and current tools, and we will price an essential or full scope with a realistic plan. 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.
