The dominant factor is never the technology stack — it remains how much is still undecided. Every open question in the requirements becomes padding in the estimate. A team that does not know the exceptions and edge cases must assume a pessimistic case. Spending a week on a discovery phase can cut the total by far more than any rate negotiation.

Third-party integrations remain another reliable source of cost. A form that saves data is low risk; the same screen wired into an old accounting system is not. The unknown hides in the third party: rate limits and sandbox access, hire typo3 developers long certification processes, fields that mean something different on each side. Ask the estimator to list every external system, since that is where the numbers slip.

The requirements nobody writes down quietly rewrite the estimate. An application used by a handful of staff has almost nothing in common with the same functionality handling thousands of external customers. Audit and compliance requirements, uptime targets, scalability, data retention rules and multi-language support all add real engineering time. Write them down at the start or else expect the estimate to move later.

Who actually does the work changes the arithmetic. A day rate says almost nothing on its own: a senior engineer at a higher rate can be less expensive in the end than two juniors who require constant review. Ask as well which roles are billed: delivery management, quality assurance, release engineering and UX design have to be done by someone, but they should be visible in the estimate.

The quoted figure is never the full cost of ownership. Expect cloud costs, paid APIs, monitoring and a maintenance allowance for every year the software development for regulated industries runs. A reasonable rule of thumb holds that any production system requires a recurring percentage of the original budget every year simply to stay current. Treating the launch as the finish line remains the most frequent planning error.