Search "how much does custom software cost UK" and you'll get the same answer from five different agencies: somewhere between £10,000 and £500,000.
That range is technically true. It's also useless if you're a 6-person business trying to work out whether a quoting tool is worth building. A range that wide isn't a quote. It's a way of avoiding one.
Here's a more useful starting point: the cost of custom software depends almost entirely on how big the job is, not on some fixed "custom software" price tag. A three-day fix for one broken process costs nothing like a six-month customer platform. Most of the guides ranking for this keyword blend both into one number, then wonder why small businesses read it and give up.
This article breaks the cost down by what you're actually building, using real day rates and real projects, so you can work out where you sit before you ask anyone for a quote.
Why the "£10k-£500k" range exists, and why it doesn't help you
The big pricing guides aren't wrong. A healthcare platform with patient records and compliance requirements does cost £80,000 and up. An enterprise system with a dozen integrations does run past £250,000.
Those numbers come from real projects. The problem is what happens when a small business reads them.
A 4-person trades company with one broken process (an enquiry inbox nobody can keep on top of, say) reads "£10,000 to £500,000" and assumes custom software isn't for them. So they buy another SaaS subscription instead, bend their process to fit it, and the actual problem never gets solved.
The range isn't dishonest. It's just answering a bigger question than the one most small businesses are asking.
The question that actually matters: how big is the job?
Custom software isn't one product with one price. It's three different kinds of job, and the cost follows the size of the job, not some universal "custom software rate."
A single tool that fixes one thing
This is a quoting tool, an enquiry board, an internal portal, a system that connects two things that don't currently talk to each other. One problem, one fix.
At AB Systems this is what we call a Focused Build: 1-5 days of development, £500 a day, fixed price agreed before we start.
A regional auction house had one inbox, three staff, and every lot enquiry re-typed by hand. Morning triage across three people took around two hours. We built a shared enquiry board that captures, tags and routes every message automatically. It was a 3-day project. Triage now takes about ten minutes, and the team took on more lots the following quarter without adding a hire.
That's a real cost for a real fix: three days, £1,500, done. No discovery deck, no 12-week timeline, no six-figure quote for a problem that was never six figures big.
Several tools sharing one record
This is where a business needs more than one fix: a system that follows a job or a client from first contact through to invoice, with each stage handled by its own piece of tooling but all of it reading from the same data.
We call this a Full Operation. It's staged, priced per stage, and something is working in the first week rather than in month four. A marketing agency we work with started with a knowledge hub and has added campaign tooling, outreach tooling and ops tooling in stages since, each one scoped and priced on its own before the next started.
The total cost here scales with how many stages you need, not with a blanket "enterprise system" rate. You can stop after stage one if that's all you need.
Something closer to a full platform
Customer-facing apps, anything with compliance requirements, anything with a lot of third-party integrations. This is where the £30,000-£150,000+ figures in the big guides genuinely apply, and where the timeline stretches to months rather than days.
Most small businesses reading a "custom software cost UK" article don't need this. They need the first category and have been told to price themselves against the third.
What a day rate actually buys you
£500 a day, one day minimum, is the AB Systems rate regardless of project size. Two things about that number matter more than the number itself.
First, it's fixed before work starts. If a build takes longer than agreed, that overrun is absorbed by us, not billed to you. Hourly billing rewards slow work. A fixed day rate doesn't.
Second, you own what gets built. No licence, no per-seat cost, no renewal. A £1,500 three-day build stays a £1,500 build. It doesn't quietly become £1,500 a year the way SaaS subscriptions do once you add users.
Compare that to the alternative most small businesses default to: an off-the-shelf tool like Monday.com or HubSpot. The subscription looks cheaper on day one. Add per-seat pricing across a growing team and five years of renewals, and a £15/month plan for eight people is £7,200 over five years, for a tool that still doesn't match your actual process. Custom software vs off-the-shelf covers that comparison in full.
A worked example: Prospect Scout
We use this one on ourselves, so the numbers are as real as it gets.
Researching which local businesses were worth calling meant hours on Google Maps, Companies House and a spreadsheet that fell out of date within a week. We built Prospect Scout: a tool that scrapes, verifies and scores every business in a town, feeding a pipeline the team actually calls from.
Build time: 2 days for the research engine, plus a further day a week later to add the CRM board. Total: 3 days, £1,500.
Result: the first run put 135 verified, scored businesses on the calling board, out of 155 researched, in the time it used to take to research one town by hand. Researching a new town went from an afternoon to a button press.
That's the pattern worth taking away. Small, specific problems have small, specific price tags. The number only gets big when the job does.
What drives the cost up (and what doesn't)
A few things genuinely add cost, and they're worth knowing before you ask for a quote:
Integrations with other systems. Connecting to Companies House, Stripe, an existing database, or a legacy system adds real work. It's a legitimate reason a quote goes up.
Compliance requirements. Healthcare, finance and anything handling sensitive personal data need extra security work and testing. That's the £80k+ tier, and it's justified when it applies to you.
Data migration. Moving years of history out of an old system or a messy spreadsheet is its own job, separate from building the new tool.
What doesn't need to add cost: agency overhead, a lengthy discovery phase for a problem you can already describe in two sentences, or a pricing model built around your business being bigger than it is. A free systems audit should tell you honestly which category your problem sits in, including telling you when the answer is to buy something off the shelf instead.
How to work out where you sit
Before asking anyone for a quote, answer three questions:
Is this one broken process, or several that share the same data? One process is a Focused Build. Several is a Full Operation, staged.
Does it touch sensitive data, payments, or an existing system you need to integrate with? If yes, expect the cost and timeline to reflect that. If no, you're likely closer to days than months.
A fix you can describe in two sentences to someone who's never seen your business doesn't need a 40-point discovery framework to scope it. It needs someone to build it.
The honest answer
Custom software in the UK costs £500 a day at AB Systems, with most single-problem fixes landing at 1-5 days: £500 to £2,500, fixed, before work starts. Multi-stage builds are priced per stage as they go. Full platforms with compliance and integration needs run into the tens of thousands, and the big pricing guides are right about that tier.
The number that matters isn't the industry range. It's the size of your actual problem. A free systems audit tells you which one you're dealing with, and gives you a fixed price or a straight answer that you don't need us at all. You can see the fixed-price structure in full on the pricing page, and more examples of real builds and their timelines on the work page.