Short answer: custom software development in the UK in 2026 costs about £15,000 to £40,000 for a focused first version, £40,000 to £120,000 for a full product with accounts, integrations and a proper backend, and £120,000 and up for platforms at scale. UK agency day rates run £400 to £900. The number is set by scope, not by the idea, and the cheapest way to get an accurate figure is a fixed-price discovery. Below is what UK businesses actually pay, what moves the number, and how to keep it down without a bad build.
What "custom software" covers
Custom software is any system built to your process rather than bought off the shelf: an internal tool that replaces spreadsheets, a customer portal, a booking and dispatch system, a web application, a SaaS product, or an integration layer between the tools you already run. The custom software development service page describes the engagement; this guide is about money.
Custom software development cost by scope (UK, 2026)
| Scope | What it includes | Typical UK cost | Timeline |
|---|---|---|---|
| Internal tool or MVP | One core workflow, a handful of screens, basic user roles, one integration | £15,000 to £40,000 | 8 to 12 weeks |
| Full product | User accounts, custom backend, several integrations, reporting, admin | £40,000 to £120,000 | 3 to 6 months |
| Platform at scale | Multi-tenant, payments, real-time features, compliance, high availability | £120,000 to £400,000+ | 6 to 12 months, phased |
| Ongoing development | A retained team improving a live product | £8,000 to £30,000 a month | Rolling |
These are industry-typical ranges for UK agencies and experienced contractors. A single freelancer will quote lower on a small tool and cannot usually take on a full product; an offshore-only team will quote lower across the board, and the difference is normally design, product management and communication rather than code quality.
What drives the cost
- Number of user types. Every role (customer, staff, admin, partner) adds screens, permissions and testing.
- Integrations. Accounting, payments, CRM, mapping, messaging, and legacy systems each add days. Integrations with old or undocumented systems add weeks.
- Data. Migrating existing records, cleaning them, and keeping two systems in sync during a transition is often a fifth of the budget.
- Design depth. A clean, functional interface built from a component library costs far less than a fully custom, animated brand experience.
- Compliance. Handling payment data, health data, or personal data at scale adds security work, audit trails and testing.
- Uncertainty. A vague brief costs more than a precise one because the team has to discover the requirements as they go. Discovery is the cheapest way to remove it.
How UK pricing models work
| Model | How it works | Best for |
|---|---|---|
| Fixed-price discovery, then fixed-price build | A short paid discovery (typically £2,000 to £8,000) produces a scope, a price and a plan | Most first builds |
| Time and materials | You pay for days used, with a monthly cap | Evolving products with an involved product owner |
| Retained team | A fixed monthly fee for a fixed capacity | Live products with a roadmap |
Whatever the model, insist on two-week sprints with a demo at the end of each. Working software every fortnight is the only honest progress report.
A worked example: a dispatch and quoting tool for a trades firm
The brief: replace three spreadsheets and a WhatsApp group with one tool where office staff create jobs, engineers see their day on a phone, quotes go out from templates, and paid invoices sync to the accounting software. Two user types, four core screens each, one accounting integration, no payments in-app. That is a first-version build at roughly £25,000 to £35,000 over ten weeks. Adding customer self-booking, card payments and a customer portal moves it into the full-product range.
Custom vs off-the-shelf
Before commissioning custom software, check whether a configured platform does the job. For CRM, follow-up and booking, a configured GoHighLevel or HubSpot build at £800 to £12,000 replaces a custom build for most service businesses. Custom earns its cost when the workflow does not fit any platform, when you need to own the code and data outright, or when the software is the product you sell.
Hidden costs to budget for
- Hosting and infrastructure: £50 to £500 a month for a small product; more with real-time features or heavy data.
- Third-party services: payment fees, SMS, maps, email sending, AI APIs, each usage-based.
- Maintenance: 15 to 20 percent of the build cost per year for updates, security patches and small changes.
- Your team's time: product decisions, testing, and content. A build with no owner on your side runs late.
How to keep the cost down
- Pay for discovery. A precise scope removes the contingency every agency adds to a vague one.
- Ship the smallest version that changes how you work. Then extend it based on what people actually use.
- Use platforms as parts. Auth, payments, email and analytics are solved; do not rebuild them.
- Own the code. Make source-code ownership, documentation and deployment access part of the contract, so you are never priced by lock-in.
Cost by type of software (UK, 2026)
| Type of software | Typical UK cost | Notes |
|---|---|---|
| Internal tool replacing spreadsheets | £15,000 to £40,000 | One or two roles, a few screens, one integration |
| Customer portal | £25,000 to £70,000 | Accounts, documents, payments, messaging |
| Booking and dispatch system | £30,000 to £80,000 | Calendars, routing, mobile-friendly staff view, notifications |
| Integration layer between existing systems | £10,000 to £40,000 | Often cheaper than replacing either system |
| SaaS product, first version | £40,000 to £120,000 | Multi-tenant, billing, onboarding, admin |
| AI feature inside an existing product | £15,000 to £60,000 plus usage | Retrieval, evaluation and guardrails are most of the work |
| Legacy system rebuild | £50,000 to £250,000 | Phased, with both systems running in parallel |
The cheapest entry on that table, the integration layer, is often the highest-value one. Two systems that finally talk to each other remove more manual work than a new system that replaces one of them.
A sample budget breakdown
For a £50,000 full-product build, a typical UK agency budget splits roughly like this:
| Phase | Share | Amount | What it buys |
|---|---|---|---|
| Discovery and scoping | 8 percent | £4,000 | Requirements, user flows, technical plan, fixed price |
| Design | 15 percent | £7,500 | Wireframes, interface design, component library |
| Development | 50 percent | £25,000 | Backend, frontend, integrations |
| Testing and QA | 12 percent | £6,000 | Automated tests, manual testing, security review |
| Project management | 10 percent | £5,000 | Sprint planning, demos, communication |
| Deployment and handover | 5 percent | £2,500 | Infrastructure, documentation, training |
If a quote shows development at 85 percent and nothing for testing or management, expect the missing 15 percent to appear later as bugs and delay.
Where budgets go wrong
- No product owner on your side. Decisions wait, sprints stall, and the team builds guesses. Name one person with the authority to decide.
- Scope added mid-build without re-pricing. Every "while you're in there" is a day. Keep a list for version two.
- Integrating with a system nobody documented. Budget a spike to investigate any legacy integration before committing to a price.
- Designing for edge cases first. Build the common path, then the exceptions the data proves exist.
- Skipping migration planning. Old data is dirtier than anyone remembers; plan a rehearsal migration.
- Treating launch as the end. A product with no maintenance budget degrades within a year as dependencies, browsers and operating systems move on.
How to compare quotes
Put every quote on the same grid: scope (what is included and what is not), team (who does the work and where), model (fixed, time and materials, retained), timeline (weeks and milestones), ownership (code, infrastructure, documentation), and what happens after launch. A quote that is half the price of the others usually differs on scope or ownership, not on efficiency. Ask each agency for two comparable projects and how long each took from kick-off to live.
Timeline expectations by scope
Timelines track scope more tightly than cost does, because a team can only be so big before it slows down. A focused first version of one workflow takes 8 to 12 weeks: two weeks of discovery and design, four to six of development in two-week sprints, two of testing and launch. A full product with several roles and integrations takes 3 to 6 months, delivered as a first release at the midpoint so the business is using it while the rest is built. A platform at scale takes 6 to 12 months and should ship in phases of six to ten weeks, each with a measurable outcome, so that the budget can be stopped or redirected at any phase boundary. Two things stretch every timeline: decisions that wait, and data that arrives late. Name a product owner with authority, and start the data work in week one.
The retained model after launch
Once a product is live, most businesses move from a project to a retained team: a fixed monthly fee for a fixed capacity, typically £8,000 to £30,000 a month for two to five people part-time, covering maintenance, small improvements and the next roadmap items. The alternative, buying changes one at a time, costs more per change and loses the team's knowledge of the codebase. A good retainer publishes a monthly summary of what shipped, what it cost, and what is next, so the spend stays visible.
Bottom line
Custom software in the UK costs from around £15,000 for a focused tool to six figures for a product at scale. The spread is scope, and scope is a decision you make before the build, not a number the agency discovers afterwards.
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