If you're a founder trying to budget for a first product or an internal tool, you've probably seen cost guides that give one big range and no reasoning behind it. This post explains what actually moves the price of custom software, how agencies price it, and the costs that show up after launch. I run SiteFusion, a software team that builds SaaS products, internal tools and customer portals for founders in the US, UK, Europe and the Gulf, so I'm describing how we and the teams we compete with put a quote together.
The short answer
The cost of custom software is mostly the number of weeks a team of a given size spends on it. Everything in this post is about what pushes that number up or down. Two products with the same feature list on paper can differ several times over in effort, depending on integrations, permissions and how settled the requirements are.
What drives the cost
Scope of the first version
The biggest lever is how much goes into version one. A product that does one job for one type of user, with a short path from signup to result, is a very different build from one that tries to match a mature competitor on day one. Most of the savings in any project come from scoping, before a line of code is written. Our custom SaaS guide covers how to scope a first version.
Integrations
Each system your software has to talk to (payment providers, CRMs, ERPs, accounting software, carrier or healthcare APIs) adds work for the connection itself, for error handling when the other side is down, and for testing. Integrations with poor documentation or no test environment cost the most, and they're the most common reason estimates slip.
Users, roles and permissions
One type of user with one role is simple. B2B software usually needs client companies with several users each, admins on the client side, and data that must never leak between accounts. That permission model touches every screen and every query, so it has a real effect on effort.
Data and compliance
If you handle payments, health data or personal data about people in the EU or UK, expect extra work for security reviews, audit logs, data retention rules and hosting choices. If you plan to sell to larger companies, their procurement teams will send security questionnaires, and some will ask for SOC 2. Building with that in mind from the start costs less than adding it later.
Design
A product built on a solid component library with a clean, standard layout costs less than one with a fully custom visual design. Both are valid. Decide which one your first customers need.
How settled the requirements are
If the requirements change every week, you're paying for discovery while you build. That's normal for an early product, but it should be priced as time and materials, and you should expect the final number to move.
How agencies price custom software
Most development partners use one of these models:
Fixed price for a fixed scope. You know the number up front, but the agency adds a margin for risk, and every change becomes a change request. It works when the scope is small and well defined.
Time and materials. You pay for the hours or weeks actually worked. It's more flexible and usually more honest for early products, but you need regular demos and a budget cap to keep it under control.
A dedicated team on a monthly retainer. You get a set team for a set monthly fee. This suits ongoing product work after the first version is live.
A paid discovery phase before any of these is worth it for most projects. It produces a written scope, a clickable prototype and an estimate based on real detail. We compare the first two models in more depth in fixed price vs time and materials.
Why quotes for the same project vary so much
Founders are often surprised when quotes for the same brief differ by a wide margin. The usual reasons:
Each agency read a vague brief differently and priced its own guess.
Some quotes include design, QA, project management and deployment, and some leave them out.
Team seniority differs. A senior team usually needs fewer weeks and makes fewer architecture mistakes that cost money later.
Some agencies quote low to win the deal and recover the difference through change requests.
The fix is a written brief that every agency prices against. We wrote a guide on how to write an MVP brief that gets accurate agency quotes. Then ask each agency to break the quote down by feature and by role, so you can compare like for like.
Costs after launch
The build is only part of the total. Budget for:
Hosting, databases, email, file storage and monitoring. These are usually small at the start and grow with usage.
Third-party services such as payment fees, maps, SMS and AI model usage. AI features in particular have a running cost per request that should be estimated before launch.
Maintenance: security updates, dependency upgrades, bug fixes and small changes as your users find gaps. Most software needs some of this every month.
New features once you know what customers use.
Our post-launch support service explains how we handle maintenance after go-live.
Build, buy or use no-code
Before you budget for custom development, check whether an existing product or a no-code tool already does what you need. For a small team with a standard workflow it often does, and that's the cheaper option. Custom software starts to make sense when the workflow is what makes your business different, when per-seat pricing gets expensive as you grow, or when you need integrations and permissions a generic tool can't handle. Our build vs buy guide goes through that decision.
How to keep the cost under control
Write down the one question the first version has to answer, and cut anything that doesn't help answer it.
Do some work by hand at first (imports, reports, onboarding) and automate it once you know it's needed.
Ask for a demo of working software every week or two.
Make decisions quickly. Waiting on the client side is one of the most common causes of overruns.
Make sure the code, the hosting and the database accounts are in your company's name from day one.
If you'd like a scoped estimate for your product, you can book a call with us. We'll ask about your users, integrations and first-version goal before giving any number. Our full-stack development service and guide to hiring a development partner have more on how we work.
Frequently asked questions
How much does it cost to build a SaaS MVP?
It depends mainly on scope, integrations and the permission model. A focused MVP for one type of customer costs far less than a product that copies a mature competitor. Get a paid discovery phase and a written scope, then compare quotes against the same document.
Is fixed price or time and materials better for a startup?
Fixed price suits a small, well-defined scope. Time and materials suits early products where requirements will change as you learn. Many teams use a fixed-price discovery phase, then time and materials with a budget cap for the build.
Why are some agency quotes much cheaper than others?
Usually because they cover less (no QA, design or deployment), assume a smaller scope, use a less experienced team, or plan to charge for changes later. Ask for a breakdown by feature and role before comparing.
What are the ongoing costs of custom software?
Hosting and infrastructure, third-party services, AI usage if your product has AI features, and maintenance such as security updates and bug fixes. Plan for these from the start so the product doesn't stall after launch.
Do I own the code if I hire an agency?
You should. Your contract should say the source code and related assets belong to your company, and the hosting, domain and database accounts should be registered to you.
Can a remote team build software for a US or UK startup?
Yes, as long as working hours overlap for regular calls, the team communicates in clear written English, and the contract covers IP ownership and data protection under the laws that apply to you.
