Custom Software Development Cost in the UK: 2026 Guide

Custom software development cost in the UK: the short answer

custom software in the UK is priced mainly by effort, so the cost is roughly the number of person-days needed multiplied by a day rate. UK contract software developers were advertised at a median of about £525 a day in the six months to mid-September 2026, so a small internal tool of 40 to 80 person-days lands around £15,000 to £50,000 in people cost, while a customer-facing platform of 250 person-days or more can pass £100,000 before hosting, support and tax effects. The bigger swings come from scope, integrations, UK GDPR work and how you treat VAT and R&D relief, not from the headline rate alone.

How UK software projects are actually priced

Almost every UK quote, whether from a freelancer, a London studio or an offshore partner, is built from the same three parts: estimated effort in person-days, a blended day rate for the team, and a contingency for unknowns. Fixed-price quotes simply hide the same arithmetic plus a risk premium.

Useful reference point: IT Jobs Watch reported a median advertised daily rate of £525 for UK software developer contracts in the six months to 16 September 2026, with the 10th percentile at £364 and the 90th percentile at £606. Those are individual contractor rates from job adverts. Agencies usually charge more per day because the rate also covers project management, QA, design, hosting set-up and their margin.

Effort is where estimates go wrong. Teams underestimate integrations with existing systems (Xero, Sage, Salesforce, HubSpot, Dynamics, bank feeds), data migration, user roles and permissions, audit trails and testing. If your specification is thin, treat any quote as a range, not a number.

Illustrative cost ranges by project type

The table below is arithmetic, not survey data: it multiplies typical effort bands by the UK contractor rate range above (£364 to £606 per day). Use it to sanity-check quotes, then replace the effort figures with your own once scope is clearer.

If you want a quicker first estimate for your own feature list, the app cost estimator breaks cost down by feature and platform.

The UK-specific factors that change the total

1. VAT on overseas development services

UK agencies that are VAT registered add 20% VAT to invoices. If you buy development services from a supplier outside the UK, the supplier normally does not charge UK VAT; instead, under HMRC's reverse charge, "it is the customer who must account for any VAT due" (HMRC VAT Place of Supply of Services manual). For a fully taxable business the output and input tax cancel out, so there is no net cost. Partly exempt businesses, common in financial services, insurance, healthcare and education, may not recover all of it, so the VAT becomes a real cost whichever supplier you choose. Check this with your accountant before comparing quotes.

2. R&D tax relief, and the overseas restriction

Some software development counts as R&D for tax purposes, typically where the project seeks an advance in technology and has to resolve genuine technical uncertainty; routine CRUD apps or configuring an off-the-shelf product usually do not. For accounting periods beginning on or after 1 April 2024, most companies claim under the merged scheme, which gives a 20% expenditure credit, while loss-making R&D-intensive SMEs (relevant R&D spend of at least 30% of total expenditure) may claim enhanced support instead (GOV.UK merged scheme guidance).

Two rules matter for build decisions. First, payments to unconnected subcontractors and externally provided workers are generally counted at 65%. Second, contracted-out R&D must usually be carried out in the UK: guidance summarised by Saffery states that undertaking R&D overseas "simply to save cost, or because workers are more readily available, will not qualify". So if a project is genuinely R&D-heavy, a lower offshore day rate may be partly offset by relief you give up. If the project is not R&D, this factor does not apply. Stratgik is a technology firm, not a tax adviser, so confirm eligibility with a qualified R&D tax specialist.

3. UK GDPR and the Data (Use and Access) Act 2025

Any system that holds personal data needs privacy work built in: access controls, data retention rules, subject access request handling, logging and processor contracts. The Data (Use and Access) Act 2025 received Royal Assent on 19 June 2025, and most of its data protection changes, including recognised legitimate interests and revised automated decision-making rules, came into force on 5 February 2026 (DLA Piper). From 19 June 2026, controllers must also provide a way to make data protection complaints, acknowledge them within 30 days and respond without undue delay (Michelmores on ICO guidance).

In practice, that means budgeting for features such as a complaints intake form, a request tracker, audit logs and clear retention settings. Adding these at the start is far cheaper than retrofitting them. Stratgik is not a law firm and this is not legal advice; for implementation help see our UK GDPR compliance page, and take legal advice on your specific obligations.

4. In-house hiring costs

Comparing an agency quote with hiring is not like-for-like. Since 6 April 2025, employer National Insurance has been 15% above a secondary threshold of £5,000 a year (Deloitte), on top of pension contributions, recruitment fees, equipment, management time and the months it takes to hire. In-house teams make sense when software is your core product and work is continuous; for a defined build, an external team is often cheaper overall.

Costs that sit outside the build quote

• Hosting and cloud: small business apps often run for tens to low hundreds of pounds a month, but data-heavy or AI features can cost far more. Ask for a monthly estimate at expected usage.
• Third-party services: email, SMS, WhatsApp Business messaging, maps, payments and AI model usage are billed per use.
• Maintenance and support: security patches, dependency upgrades, OS and browser changes, and bug fixes. Agree a support plan and response times before launch.
• Security testing: penetration testing is commonly required by larger customers, insurers or procurement teams.
• Change requests: scope added mid-build is the most common cause of overspend.

Build, buy or configure?

Before paying for custom software, check whether an existing SaaS product covers 80% of the need. Buying is usually cheaper and faster for standard functions such as accounting, HR or basic CRM. Custom builds pay off when the workflow is a genuine differentiator, when you are paying for many seats of several tools that do not talk to each other, or when integration and data ownership matter. Our free build vs buy tool walks through that decision, and a short technology decision sprint can firm up scope before you commit a budget.

Checklist: getting an accurate UK software quote

• Write down the problem, the users and the three outcomes that define success.
• List every system the software must connect to, and who owns each one.
• Separate must-have features for version one from later phases.
• Ask each supplier for effort in person-days per feature, not just a total price.
• Confirm who owns the source code, designs and IP on payment.
• Ask how UK GDPR requirements (access, retention, complaints, logging) are handled.
• Check the VAT position of each supplier with your accountant (UK VAT vs reverse charge).
• If R&D relief is part of your plan, confirm where the work will be done and take specialist advice.
• Get a monthly running-cost estimate for hosting and third-party services.
• Agree a support and maintenance plan, including response times, before launch.
• Keep a 15–20% contingency for unknowns.

Frequently asked questions

How much does a simple custom app cost in the UK?

A simple internal tool of around 40 to 80 person-days works out at roughly £15,000 to £50,000 in people cost at current UK contractor rates. Agencies may quote higher because their day rate includes management, testing and design.

What is the typical UK day rate for a software developer?

IT Jobs Watch reported a median advertised contract rate of £525 a day for UK software developers in the six months to 16 September 2026, with most adverts between £364 and £606. Specialist and London roles can be higher.

Is it cheaper to use an offshore development team?

Day rates are usually lower offshore, but compare the full picture: communication overhead, time zones, IP terms, UK GDPR data transfer arrangements, VAT treatment and, for genuine R&D projects, the fact that overseas subcontracted R&D generally does not qualify for UK relief on cost grounds alone.

Does custom software development qualify for R&D tax relief?

Only if the project seeks an advance in science or technology and resolves technical uncertainty. Many business apps do not qualify. Under the merged scheme the credit is 20% of qualifying expenditure. Stratgik is not a tax adviser, so check with a specialist.

How long does custom software take to build?

Divide effort by team size. A 120 person-day project with a team of three takes around eight to ten weeks including testing and reviews. Integrations, approvals and data migration usually add time.

Do I need to budget for UK GDPR work?

Yes, if the system holds personal data. Budget for access controls, retention settings, request handling, audit logging and, since 19 June 2026, a clear route for data protection complaints.

If you are planning a build for a UK business, start with our UK hub or see how we approach custom software projects, from scoping through to support.