What Actually Drives Software Development Costs
The dominant factor is never the choice of framework — it is almost always uncertainty. Every open question in the brief turns into padding inside the number you receive. A team that cannot see the edge cases must assume the worst. Investing a few days in a discovery phase frequently cuts the total by far more than any rate negotiation.
Connections to other systems tend to be the second big multiplier. A form that saves data is predictable; the same screen talking to a payment provider and a CRM is another matter entirely. The unknown sits in the other system: rate limits and sandbox access, long certification processes, fields that mean something different on each side. Ask any vendor to break integrations out as separate items, because this is the usual source of overruns.
The requirements nobody writes down quietly rewrite the number. A tool used by a small internal team is a very different build from the same feature set handling a hundred thousand users. Security reviews, availability guarantees, load handling, data retention rules and localisation each add real engineering time. Put them in the brief or you can expect them to arrive later as change requests.
Who actually does the work matters a great deal. A day rate reveals almost nothing on its own: one senior developer at a premium rate frequently turns out to be less expensive in the end than a pair of junior developers who require constant review. Also ask who else is billed: coordination, QA, DevOps and analysis have to be done by someone, but they should be visible in the software development cost estimate.
The number in the proposal is never what you will actually spend. Plan for cloud costs, paid APIs, logging and alerting and an ongoing support budget annually. A common working assumption is that a live system needs a noticeable fraction of the initial investment annually for updates, build vs buy software security patches and small improvements. Leaving it out of the budget is the classic mistake.