If you've asked three UK agencies to quote a web app, you've probably received three wildly different numbers. One came in at £8,000. One at £35,000. One at £85,000. All for what sounds like the same project.
This isn't unusual — and it's not necessarily dishonest. Web app development costs vary enormously based on factors that aren't always obvious from the outside. This guide breaks down what's actually driving those numbers.
The Short Answer
A simple web app (user authentication, a core workflow, basic dashboard) built by a competent remote team: £3,000–£12,000.
The same app built by a mid-size London agency: £25,000–£60,000.
The same app built by a large UK agency with account managers, project managers, and a design team: £60,000–£150,000+.
The code is often identical. What you're paying for changes dramatically.
What Actually Drives Web App Cost
1. Complexity of the Core Feature
This is the biggest variable. A web app that lets users log in and view a dashboard is fundamentally different from one that processes payments, integrates with third-party APIs, handles real-time data, or manages complex user permissions.
Low complexity (£3,000–£8,000):
- User authentication
- CRUD operations (create, read, update, delete records)
- Simple dashboard with static data
- Basic email notifications
- Stripe payment integration
Medium complexity (£8,000–£25,000):
- Real-time features (live updates, notifications)
- Complex user roles and permissions
- Multiple third-party API integrations
- File uploads and processing
- Advanced search and filtering
- Multi-tenant architecture (SaaS with multiple organisations)
High complexity (£25,000+):
- Custom algorithms or data processing
- Machine learning or AI features
- Complex financial calculations
- Regulatory compliance requirements (GDPR, FCA, NHS)
- High-availability infrastructure requirements
2. Who's Building It
This is where the biggest cost differences come from — not the complexity of the work, but the overhead of the team doing it.
Large UK agency: You're paying for a sales team, account managers, project managers, senior developers, junior developers, QA testers, and a design team. Each layer adds cost. The actual developer writing your code might be a junior on £35,000/year. You're paying £150/hour for the privilege of that overhead.
Mid-size UK agency: Leaner, but still carries significant overhead. Typically £80–£120/hour. Better value than large agencies, but still expensive for straightforward builds.
Specialist remote team: Direct access to senior developers. No account managers, no unnecessary overhead. Typically £40–£70/hour equivalent. The work quality is identical — the cost structure is different.
Freelancer: Cheapest day rate, but single point of failure. If they get sick, take another project, or disappear, your project stops. No backup, no process, no accountability structure.
3. Design
A web app needs UX design — how users navigate, what they see on each screen, how errors are communicated. This is often quoted separately and can add £2,000–£15,000 depending on scope.
What's worth paying for:
- User flow mapping (how users move through the app)
- Wireframes for key screens
- A consistent component library
What's often not worth paying for at MVP stage:
- Pixel-perfect Figma designs for every possible state
- Custom illustration or animation
- Full brand identity work (do this separately)
4. Infrastructure and DevOps
Where does the app live? How does it deploy? How does it scale?
For most early-stage web apps, the answer is simple: Vercel or Railway for hosting, Supabase or PlanetScale for the database, Cloudflare for CDN. Total cost: £0–£50/month. Setup time: half a day.
Some agencies quote £5,000–£15,000 for "infrastructure setup" that amounts to clicking through a few dashboards. Unless you have specific compliance requirements (NHS data, FCA regulation, enterprise security), you don't need custom infrastructure at v1.
5. Post-Launch Support
Most agencies include a 30–90 day warranty period for bug fixes. After that, ongoing support is typically quoted as a monthly retainer (£500–£3,000/month) or hourly (£60–£150/hour).
For early-stage products, a better model is: pay for development, own the code, hire support as needed. Don't lock yourself into a retainer before you know what you actually need.
A Realistic Budget Guide
| Project Type | Remote Team | UK Agency | |---|---|---| | Landing page + waitlist | £300–£600 | £1,500–£4,000 | | Simple web app (auth + core feature) | £3,000–£8,000 | £15,000–£35,000 | | SaaS MVP (multi-tenant, billing) | £6,000–£15,000 | £30,000–£70,000 | | Complex platform (real-time, integrations) | £15,000–£40,000 | £60,000–£150,000+ |
These are honest ranges. The remote team column assumes a senior developer with a structured process — not a cheap freelancer from a bidding platform.
What to Ask Before Signing Anything
1. Who will actually be writing the code? At large agencies, the person who sold you the project is rarely the person building it. Ask to meet the developer assigned to your project.
2. What does the handover look like? At the end of the project, you should receive: full source code in a repository you own, deployment credentials, documentation for the key systems, and a walkthrough of how to make basic changes.
3. What's in scope and what isn't? Get a written list of deliverables. "Web app with user accounts and dashboard" is not a scope. "User registration, email verification, login, password reset, dashboard showing X data, ability to do Y action" is a scope.
4. What happens if the project runs over? Fixed-price projects protect you from scope creep. Time-and-materials projects protect the agency. Know which model you're on before you start.
5. Can I see examples of similar projects you've shipped? Live URLs, not screenshots. Visit them on your phone. Check the loading speed. If a developer can't show you live work, that's a signal.
The Hidden Cost of Cheap
The cheapest quote is rarely the cheapest outcome. A £2,000 web app that takes 6 months to deliver, doesn't work on mobile, and can't be maintained by anyone else will cost you far more than a £6,000 app that ships in 8 weeks and is built on a clean, documented codebase.
The real cost of a web app isn't the development invoice. It's the opportunity cost of not having it, the cost of rebuilding when the cheap version fails, and the cost of the customers you didn't convert while you were waiting.
Build it right the first time. It's almost always cheaper.
