The dominant factor is not the choice of framework — it is how much is still undecided. Every open question in the specification turns into a contingency in the estimate. A team that cannot see the exceptions and edge cases has to assume the worst. Putting two weeks into a discovery phase often reduces the overall figure by far more than haggling over hourly rates.

Integrations remain another reliable source of cost. A feature that touches only your own data is predictable; the same feature connected to a legacy ERP is not. The unknown sits in the counterparty: rate limits and sandbox access, slow approval cycles, 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 quietly rewrite the estimate. An application used by a small internal team is a very different build from the same functionality handling a hundred thousand users. Security reviews, availability guarantees, performance under load, audit logging time and materials contract accessibility all add measurable effort. Put them in the brief or you can expect them priced as extras.

Who actually does the work matters a great deal. A rate card tells you almost nothing on its own: an experienced engineer at a higher rate frequently turns out to be cheaper per delivered feature than a pair of junior developers who need constant review. Check too which roles are billed: project management, testing, infrastructure work and design have to be done by someone, but these should be itemised.

The quoted figure is not what you will actually spend. Expect hosting, subscriptions and licences, logging and alerting and a change budget for every year the software development company in uk runs. A common working assumption holds that software in active use needs a noticeable fraction of the initial investment every year in fixes, updates and small changes. Ignoring this remains the most common budgeting mistake.