How much does replacing a legacy system cost in the UK?
At Proctor Digital the ranges we actually quote are: £6,000–£15,000 for a small single-purpose system (a handful of screens, one clean data source); £15,000–£40,000 for a typical line-of-business system covering orders, quotes, stock and reporting; and £40,000–£90,000+ for larger multi-department estates, delivered in phases. Every quote includes parallel running, rehearsed data migration and training; none involves a big-bang cutover. The starting point is free: a 30-minute Legacy Risk Audit with a one-page written summary. Four things move the price: screens and workflows, data quality, integrations, and compliance needs. Most UK SMEs can also write the cost off in year one under the £1 million Annual Investment Allowance.
Between £6,000 and £90,000, and anyone who names one figure without asking questions first is guessing. These are the ranges we actually quote at Proctor Digital as of July 2026, what moves a system up or down within them, and what the number includes.
The answer in one paragraph
At Proctor Digital the ranges we actually quote are: £6,000–£15,000 for a small single-purpose system, meaning a handful of screens over one clean data source; £15,000–£40,000 for a typical line-of-business system, the order processing, quoting, stock and reporting software a firm runs its day on; and £40,000–£90,000+ for larger multi-department estates, always phased. The starting point costs nothing: a free Legacy Risk Audit, which is a 30-minute call followed by a one-page written summary. These are our own quoting anchors rather than market statistics; a large agency will quote multiples of them, and the reasons are structural rather than sinister, as covered below. Every figure includes data migration with rehearsals, parallel running against the old system, and training, because a replacement nobody trusts on day one is not a replacement.
The ranges we actually quote
| System size | What that looks like | Our range | Typical timeline |
|---|---|---|---|
| Legacy Risk Audit | A 30-minute call and a one-page written risk summary | £0 | Within a week of first contact |
| Small single-purpose system | A handful of screens, one clean data source: a quoting tool, a job book, a booking diary | £6,000–£15,000 | 4–8 weeks |
| Typical line-of-business system | Order processing, quotes, stock and reporting: the system the office lives in all day | £15,000–£40,000 | 2–4 months |
| Larger multi-department estate | Several linked modules, multiple integrations, more than one department with opinions | £40,000–£90,000+ | 4–9 months, phased |
Two notes on how we use that table. First, the ranges are for rebuilding what the business actually uses, which is routinely smaller than what the old system nominally contains; twenty years of menus accumulate screens nobody has opened in a decade, and we do not charge to recreate them. Second, we quote fixed prices after seeing the system, not open-ended day rates. The point of replacing a legacy system is to remove uncertainty, and a quote that grows as the work does would be a strange way to start.
The four things that move the price
Screens and workflows. The best single predictor. A quoting tool with six screens is a different job from an operations system with forty, and counting them honestly is the first thing we do. Reports count too: every printout, export and month-end routine is a screen by another name.
Data quality. A clean SQL Server database migrates routinely and sits at the bottom of each range. Decades of Access, dBASE or proprietary flat files, with validation living in old code and meanings drifted away from field names, need rehearsal: trial migration, reconciliation, correction, repeat. Data is the least visible cost driver and the least skippable.
Integrations. The accounts package, the courier, the website, a supplier feed: each is a moving part the new system must speak to correctly, and each adds design, testing and a failure mode to handle. A system that talks to nothing is cheaper than the same system with three integrations.
Compliance and audit needs. Audit trails, role-based permissions, retention rules, sign-off workflows: businesses that answer to a regulator or an auditor sit toward the top of each range, not because the software is harder to write, but because proving it behaves is part of the job.
What every quote includes
The number covers the whole job, not the software alone.
- Parallel running: the old system stays live while the new one earns trust beside it, the approach described in migration without downtime.
- Data migration with dry runs: we rehearse the migration until the reconciliation is boring, and only then do it for real.
- Training and handover: staff working confidently before the old system is retired, plus documentation and full access, so there is no dependency on us by design.
- No big-bang cutover: we do not switch a business over on a Friday night and hope. That habit is how legacy horror stories begin.
If a quote you are comparing excludes migration, training or a parallel period, it is a quote for less than the job.
The number to weigh it against
The alternative to spending is not £0. Legacy systems bill quietly: the spreadsheet workarounds that patch the gaps and get re-keyed into the real system; the one member of staff who knows how month-end actually runs; the retired developer whose phone number is the real support contract, a situation we described in our software developer retired. And somewhere in the building there is one beige PC that must never be switched off, and everyone knows which socket it lives in. We worked through this arithmetic in the true cost of keeping a DOS-era system alive; the short version is that a “free” incumbent system charges in staff time, key-person risk and missed work, just never by invoice, which is why it wins every budget meeting until the day it fails.
Tax relief and grants
Two things soften the figure for UK SMEs. The first is the Annual Investment Allowance, permanent at £1 million, which lets most SMEs write off qualifying capitalised software against profits in the year the money is spent rather than depreciating it over years; for a profitable firm, that makes the after-tax cost of a rebuild materially lower than the headline. Confirm the treatment with your accountant, since it depends on how the spend is capitalised. The second is grant funding, which is patchier: the national Help to Grow: Digital scheme closed in February 2023, and what remains is regional and sector-specific, changing too often to restate here. We keep a live round-up in UK digitalisation grants in 2026, which is the better place to check what applies to your area.
Getting a number for your system
Ranges are honest, but your system deserves a figure, and reaching one costs nothing. The free Legacy Risk Audit is a 30-minute call about what you run and what it touches, followed by a one-page written summary of risks and options. If a rebuild makes sense, a fixed quote follows, built from your actual screens, data and integrations. If staying put is the sensible answer for now, the summary says that instead, and we part on good terms. How we approach the work, platform by platform, is set out on the legacy rescue page.