The dominant factor is not the technology stack — it is uncertainty. Each unanswered question in the specification is converted into a buffer inside the number you receive. A team that does not know the edge cases has to assume the worst. Spending a week on a discovery phase frequently cuts the final cost by far more than any rate negotiation.

Third-party integrations tend to be another reliable source of cost. A form that saves data is easy to estimate; the same screen wired into a legacy ERP is another matter entirely. The cost hides in the third party: poor documentation, long certification processes, data that does not match your model. Ask any vendor to break integrations out as separate items, as this is where estimates break.

The requirements nobody writes down silently change the number. An application used by a small internal team is a very different build from the same functionality handling thousands of external customers. Compliance work, uptime targets, scalability, data retention rules and multi-language support all add measurable effort. Put them in the brief or else expect them priced as extras.

Who actually does the work matters. A rate card says almost nothing on its own: one senior developer at twice the price frequently turns out to be less expensive in the end than a pair of junior hire dedicated angular developers who need heavy code review. Ask as well who else is billed: kotlin app development company project management, testing, DevOps and UX design have to be done by someone, but they should be itemised.

The build price is never the total cost. Plan for cloud costs, subscriptions and licences, monitoring and a maintenance allowance for every year the software development staff augmentation runs. A useful planning figure says that custom software development pricing in active use requires a meaningful share of the original budget every year for updates, security patches and small improvements. Ignoring this remains the classic mistake.