Custom software development cost: what drives the price and how to estimate it

Off-the-shelf software is cheap until your process does not fit it. Then you pay in workarounds, spreadsheets and manual copy-paste between systems. At that point custom software development becomes an option, and the first thing everyone wants to know is the price. The honest answer is a range, but the range can be narrowed quickly if you know what drives it.

We build and maintain custom systems for clients: billing and payment integrations, customer portals, internal tools and multilingual sites. Below is how we estimate projects and what we tell clients before they sign anything.

What drives the cost of custom software

Every estimate is built from the same few factors:

• Scope. The number of screens, user roles, workflows and reports. Each feature has to be designed, built, tested and maintained. Scope is the single biggest driver and the one you control most.
• Complexity of business rules. A form that saves data is cheap. A pricing engine with discounts, taxes, currencies and exceptions is not, even if it looks like one screen.
• Integrations. Payments, CRM, ERP, accounting, shipping, email and messaging. Each external system adds authentication, error handling, retries and testing against someone else's API. Well-documented APIs are quick; legacy systems without an API are slow.
• Data migration. Moving years of records from spreadsheets or an old system, cleaning duplicates and mapping fields often takes longer than expected.
• Design and UX. A clean admin interface on a standard component kit costs far less than a custom-designed customer-facing product.
• Non-functional requirements. Security, performance under load, availability, audit logs, accessibility, multiple languages and compliance (GDPR, payment rules) all add effort.
• Team location and rate. Hourly rates differ several times between regions and between a freelancer, a small studio and a large agency. A higher rate with fewer hours can be cheaper overall.

Typical cost ranges by project type

These are rough orders of magnitude for a small, experienced European team charging roughly €40-100 per hour. Treat them as a sanity check, not a quote.

• Integration between existing systems: €2k-20k. For example, syncing orders from your shop to accounting, connecting a payment provider or pushing leads from forms into a CRM. Price depends on the number of systems, data volume and how good their APIs are.
• Internal tool or admin panel: €5k-30k. A dashboard, an approval workflow, a booking or inventory tool for your team. Staff can live with a simple interface, so design costs stay low.
• Customer portal: €15k-60k. Accounts, roles, documents, payments, notifications and integration with your back office. Security and UX matter more because customers use it.
• SaaS product MVP: €30k-120k and more. Multi-tenant architecture, subscriptions and billing, onboarding, admin tools, analytics and a polished interface. The range is wide because "MVP" means very different things to different founders.
• Taking over and modernizing existing software: varies. Start with an audit; the cost depends on code quality, test coverage and documentation. Our legacy PHP handover guide describes how to take over a project safely.

If an estimate is far below these ranges, ask what is missing: testing, deployment, documentation or support. If it is far above, ask which features drive the number and whether they are needed for the first release.

Hourly vs fixed price vs retainer

• Hourly (time and materials). You pay for actual hours, usually with weekly reports. Best when the scope is not fully known, priorities change or you are improving an existing system. The risk of overruns is managed with a budget cap and regular reviews.
• Fixed price. One price for a precisely defined scope. Best for small, well-specified projects. Expect the vendor to add a risk margin, and expect change requests to be priced separately. A fixed price without a detailed specification usually ends in disputes.
• Retainer. A monthly block of hours for ongoing development, maintenance and support. Best after launch, when there is a steady stream of improvements, updates and small fixes. It also guarantees that someone who knows the system is available.

Many projects combine them: a fixed-price discovery phase, hourly development of the first release, then a retainer for support.

Hidden costs to include in your budget

• Hosting and infrastructure: servers or cloud, databases, backups, CDN, monitoring and domain and email services.
• Third-party services: payment provider fees, SMS and email sending, maps, AI model APIs and paid libraries.
• Maintenance: security patches, framework and language upgrades, fixes after browser or API changes. A common rule of thumb is 15-20% of the initial build cost per year.
• Change requests: real users will ask for changes in the first months. Reserve 10-20% of the budget for them.
• Your own team's time: answering questions, testing, preparing content and data. Projects stall when nobody on the client side has time for decisions.
• Exit costs: make sure you own the code, have access to the repository and servers and receive documentation, so changing vendors later does not mean starting over.

How to reduce the cost without cutting quality

1. Pay for discovery first. A short architecture analysis turns a vague idea into a list of features, integrations and risks. It is the cheapest way to get an accurate estimate and avoid building the wrong thing.
2. Cut the first release to the core workflow. Launch with the features that make or save money, and add the rest based on real usage.
3. Reuse instead of rebuilding. Use proven services for payments, authentication, email and search. Check whether a no-code tool can handle part of the job; our article when no-code breaks explains where the limits are.
4. Use a standard admin interface. Custom design belongs on customer-facing screens, not on every internal form.
5. Automate testing and deployment early. It costs a little at the start and saves a lot on every later change.
6. Decide quickly. Waiting weeks for approvals keeps the team context-switching and the hours growing.

How to get an estimate you can trust

Prepare a short brief: the business problem, the users and roles, the main workflows step by step, the systems to integrate with, examples of documents or data, any deadlines and your budget range. Sharing a budget range is not a weakness; it lets the developer propose the best solution for that amount instead of guessing. Ask every vendor to break the estimate down by feature and to list assumptions and exclusions. Compare those lists, not just the totals.

How we can help

We build custom software, integrations and customer portals, and we take over existing PHP projects. To get a realistic number before you commit, book a consultation (€50/hour) or order an architecture analysis (€200): a written breakdown of features, integrations, risks and an estimate. See our integrations service and the PebbleHost billing case study for an example of a custom billing integration in production.