How Much Does a Custom Web Application Cost in the UK?

"Web application" covers everything from a booking form to a system that runs a company. The price range is correspondingly wide, which is why most agencies will not put a number on a page. Here are the numbers, with the reasoning attached.

What counts as a web application

A website presents information. A web application does work: it has logins, it stores and changes data, it does something different for each user. Client portals, booking and scheduling systems, quoting tools, internal dashboards and stock systems are all web applications. If your brief includes the words "log in" or "each customer can see their own", you are buying an application, and it is priced differently from a website.

We build these as part of our custom web app development work, mostly in PHP and React, hosted in the UK, with the code handed over at the end.

UK price bands in 2026

• £6,000 to £15,000 - a single-purpose tool: a booking system with availability and payments, a simple client portal showing documents and invoices, a quoting calculator. One or two user types. 4 to 8 weeks.
• £15,000 to £40,000 - a system with several roles, a workflow (things move through stages, people get notified), integration with accounting or email, and reporting. This is where most internal tools and customer portals land. 8 to 14 weeks.
• £40,000 to £100,000+ - a platform: many user types, public sign-up, payments and subscriptions, third-party integrations, an API for partners, or a mobile app alongside. 14 weeks upwards, delivered in phases.

These assume a UK team. London day rates push the same scope 30 to 50 percent higher. Very low quotes usually mean a template being bent into shape, which works until the first change request.

The questions that pin the number down

A good scoping call is mostly questions. These are the ones that change the quote most:

Who logs in, and what can each of them do?

Two roles is simple. Five roles with overlapping permissions is a permissions system, and permissions systems are where projects quietly grow. Write down every type of person who will use it and the three things each of them needs to do.

What has to happen automatically?

Emails when a status changes, reminders before a deadline, documents generated from data, invoices raised in your accounting system. Each automation is cheap on its own and expensive in aggregate, because each one needs a rule, an exception path and a test.

Where does the data come from today?

If the answer is "spreadsheets", ask how many and how consistent. Migration is the line item most often missing from a first quote. We covered why in the custom CRM cost guide, and the same applies here.

Does it need to work on a phone?

Responsive design is standard and adds nothing. A native app is a separate product with its own cost, covered in our app development cost guide. Most "we need an app" requirements are met by a web application that works well on a phone.

Where the money goes

On a typical mid-band project, roughly a fifth of the budget goes on discovery and design, half on development, a fifth on testing and migration, and the remainder on launch, training and the support window. If a quote is almost entirely development with a token amount for testing, the testing will happen on your live system after launch.

Common ways the price goes up after signing

• "Can it also..." - scope added mid-build. A fixed quote should come with a change process and a rate card, so additions are priced rather than argued about.
• Integrations that turn out to have no API. Ask the agency to confirm each integration is technically feasible before signing, not after.
• Data that is worse than anyone thought. Give the agency a real export before they quote migration.
• Design revisions without a limit. Two rounds is normal. Unlimited is a sign the agency has not done this before.

Custom, low-code or off-the-shelf?

Not every application needs to be built. Low-code platforms are fast for internal tools with simple logic, and expensive per user once you scale. SaaS products cover common cases well. We wrote a decision guide in bespoke versus off-the-shelf; the short version is that you build when the process is the competitive advantage, and buy when it is not.

Three examples, priced

A quoting tool for a manufacturer

Sales staff enter specifications, the system calculates price from materials, labour and margin rules, generates a PDF quote, and records it against the customer. One role, one integration (accounting, for won quotes), no migration. Lower band: around £8,000 to £12,000, six weeks. The pricing rules are the whole project; the screens are simple.

A customer portal for an accountancy practice

Clients log in to see documents, sign engagement letters, upload records, view and pay invoices, and message their accountant. Staff manage requests and deadlines. Two roles, three integrations (practice management, accounting, e-signature), migration of existing document archives. Mid band: £20,000 to £30,000, ten to twelve weeks. Our client portal guide goes into the feature choices.

A scheduling and job management system for a field services company

Office staff schedule jobs, engineers see their day on a phone, complete job sheets with photos and signatures offline, and the office invoices from completed jobs automatically. Three roles, offline mobile use, accounting integration, migration from paper and spreadsheets. Upper band: £40,000 to £60,000, fourteen to eighteen weeks in phases. The offline mobile requirement is what moves it up.

Timeline, realistically

Discovery and design: two to three weeks, with your time needed for workshops. Development: the bulk, in two-week increments you can see working. Testing and migration rehearsal: two weeks, with your staff involved. Launch: a day, with a rollback plan. Support window: four to eight weeks of fast fixes. The elapsed time is set as much by how quickly decisions come back from your side as by the agency's speed; projects that name one decision-maker finish on time.

How to keep the price where it was quoted

Freeze scope after discovery and put every new idea into a phase-two list rather than the current build. Give the agency real data early. Nominate one person to answer questions within a day. Test when asked, not after launch. Every one of these is about your side of the project, and they are the difference between a fixed price that holds and one that does not.

If you have a brief, or half of one, send it over. We come back within a working day with a view on scope, timeline and cost, including whether it should be built at all.

Want a starting figure now? Try the instant price estimator - set a budget, pick a platform, and see where you land before you send us the brief.