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Choose what you need and see a realistic UK price range, build time and monthly running cost in seconds. Every assumption is published below, and the day rate comes from live UK contract data.
Updated 5 November 2026 · Day rates from IT Jobs Watch · Built by the engineers at SystemNexa
The short answer
In the UK in 2026, a custom web application typically costs £12,500 to £18,000 for an internal tool, £29,000 to £42,000 for a customer portal or booking system, and £38,500 to £56,000 for the first version of a SaaS product, excluding VAT. These figures use the UK median full-stack contract rate of £500 a day. User roles, payments and integrations move the price more than the number of pages.
Free written estimate
Send us your selections and a few lines about the project. A senior engineer, not a salesperson, will reply within one working day with:
Your current estimate: £29,000 to £42,000. No obligation, and we never share your details.
Benchmarks
Calculated with this tool at the UK median day rate of £500. Use them as a starting point, then adjust the calculator to your own scope.
| Project | Typical scope | Effort | Build cost | Timeline |
|---|---|---|---|---|
| Internal tool replacing spreadsheets | 2 user roles, admin and reports, search, file uploads | 25 to 36 days | £12,500 to £18,000 | 5 to 8 weeks |
| Customer portal or booking system | 2 user roles, payments, bookings, admin, notifications, 1 integration | 58 to 84 days | £29,000 to £42,000 | 9 to 16 weeks |
| SaaS product, first version | 3 user roles, subscriptions, admin, notifications, files, search, 2 integrations | 77 to 112 days | £38,500 to £56,000 | 11 to 21 weeks |
| Marketplace, first version | 3 user roles, payments, admin, notifications, search, maps, 2 integrations | 91 to 132 days | £45,500 to £66,000 | 13 to 24 weeks |
Methodology
The estimate is effort multiplied by a day rate, the same way most suppliers build a quote. Here is every number it uses.
| Project type | Days | Includes |
|---|---|---|
| Internal tool | 8 | Replace spreadsheets or a manual process for your team |
| Customer portal or booking system | 15 | Customers sign in, book, pay or track something |
| SaaS product | 25 | Many customer organisations, each with their own account |
| Marketplace | 35 | Two sides, such as buyers and sellers, matched by your platform |
| Feature | Days | Covers |
|---|---|---|
| Online payments | 6 | Checkout, refunds, receipts, deposits |
| Subscriptions | 6 | Recurring plans, upgrades, failed payments |
| Bookings and availability | 8 | Calendars, slots, capacity, reminders |
| Admin dashboard and reports | 6 | Manage records, exports, key numbers |
| Email and SMS notifications | 3 | Confirmations, alerts, reminders |
| File uploads and documents | 3 | Uploads, PDFs, generated documents |
| Search and filtering | 3 | Find records quickly across large lists |
| Maps and distance pricing | 5 | Addresses, routes, price by distance |
| Multiple languages | 5 | Translated interface and content |
| AI features | 8 | Assistants, summaries, document reading |
| Choice | Days |
|---|---|
| 1 user role | 0 |
| 2 user roles | 4 |
| 3 user roles | 9 |
| 4+ user roles | 15 |
| Each integration | 4 |
| Data migration from spreadsheets | 3 |
| Data migration from an old system | 8 |
| Choice | Extra days | Multiplier |
|---|---|---|
| Clean and consistent design | 0 | ×1 |
| Branded design design | 5 | ×1.1 |
| Bespoke design design | 10 | ×1.2 |
| Web app | 0 | ×1 |
| Installable web app | 5 | ×1 |
| Web plus iOS and Android apps | 0 | ×1.4 |
| Standard assurance | 0 | ×1 |
| Enhanced assurance | 0 | ×1.15 |
| Regulated assurance | 0 | ×1.25 |
The default rate is the median advertised UK contract rate for a full-stack developer, reported by IT Jobs Watch for the six months to 5 November 2026: £425 at the 25th percentile, £500 at the median, £570 at the 75th and £651 at the 90th. These are rates for individual contractors. Agencies that include design, project management and testing usually charge more per day, so move the slider to match the supplier you are comparing.
Timelines assume around one and a half people working on the build, plus one to two weeks for discovery and launch. Upkeep assumes half a day to a day a month for small applications, one to two days for medium ones, and two to four days for large ones, covering security updates, monitoring, backups and small changes. Hosting and third-party services are extra. Our guide to website and web application maintenance costs explains these in detail.
Go deeper
Talk to an engineer
We design, build and look after custom web applications for UK businesses, from booking platforms to internal tools. Tell us what you need and we will reply within one working day with a written estimate and an honest view of whether bespoke software is the right answer.
FAQ
Using the UK median full-stack contract rate of £500 a day (IT Jobs Watch, six months to 5 November 2026), a focused internal tool typically costs £12,500 to £18,000, a customer portal or booking system £29,000 to £42,000, and a first version of a SaaS product £38,500 to £56,000, excluding VAT. The biggest drivers are the number of user roles, payments and integrations.
It gives a planning range, not a quote. The range runs from 10% below to 30% above the central estimate, because early briefs usually grow rather than shrink. Every assumption is published on this page, so you can see exactly how the number is produced and adjust the day rate to match the supplier you are speaking to.
A focused internal tool usually takes 5 to 8 weeks, and a customer portal or booking system 9 to 16 weeks, including a short discovery phase and launch. Integrations with other systems and late changes to scope are the most common causes of delay.
Expect hosting and third-party services, often tens of pounds a month for a modest application, plus time for security updates, monitoring and small changes. The calculator shows an upkeep figure based on half a day to four days of developer time a month, depending on the size of the application.
Suppliers price different scopes and use different day rates. One quote may include design, testing, project management and a support period, while another covers development only. Ask each supplier to break their quote into the same headings, such as those in this calculator, before comparing them.
Usually, yes. Launching the workflow that saves the most time or earns the most money first, then adding features with real usage data, reduces risk and spreads the cost. The calculator suggests a first-release range whenever your selections include optional extras.
