Professional Fees Calculator

Professional fees for a UK extension usually land between the low thousands and the mid thousands of pounds, on top of the builder's price. For a standard single-storey job, an architect charges around £1,500 – £2,500 across all six design stages, a structural engineer adds £500 – £1,500, and building control takes £300 – £900. Add the planning fee and, if it applies, a party wall surveyor, and you have the full professional bill before a single brick is laid.

This calculator totals those fees for you. Pick your extension type and size, tick whether you need planning permission and a party wall agreement, and it splits the result across each professional so you can see where the money goes.

What each professional charges

The five fees behave differently, so it helps to see them apart:

• Architect: £1,500 – £2,500 for a single-storey extension, covering outline drawings, detailed plans, the planning submission, building control documents, and structural coordination. Many practices structure this around the RIBA Work Stages, so you can pay stage by stage rather than all at once. An architectural technologist often does the same job for less.
• Structural engineer: £500 – £1,500 for the calculations that size your steels, foundations, and load paths. Some architects bundle this, some do not, so ask upfront.
• Building control: £300 – £900 for a full plans application, scaled by floor area and local authority.
• Planning application: £548 in England, but only if your extension needs permission. Under permitted development you pay nothing here.
• Party wall surveyor: £700 – £1,500 per neighbour, and only if you build close to a boundary and the neighbour dissents.

The architect and structural engineer fees rise with a bigger or more complex extension. A side return, wrap-around, or double storey means more drawing and more calculation, so the calculator scales those two lines up accordingly. The planning fee is fixed, and building control moves mainly with floor area.

When you can drop a fee

Two of the five lines are conditional. If your extension stays inside permitted development limits, the planning fee falls away entirely, though the party wall rules and building control still apply. And the party wall fee only appears if you excavate or build within three metres of an adjoining owner's boundary and they choose not to consent in writing. A semi-detached home usually deals with one neighbour; a mid-terrace or a rear extension abutting two gardens can carry the cost twice.

A worked example

Take a single-storey rear extension of around thirty square metres that needs planning permission but no party wall agreement. The architect line comes in near £1,500 – £2,500, the structural engineer adds £500 – £1,500, building control charges £300 – £900, and the planning application is £548. The calculator adds those together and shows the total in the result above, then splits it into a pie chart so you can see which professional takes the biggest share.

Remember that none of this is the builder's own construction quote. These fees are already counted inside whole-project per-m² benchmarks such as £2,200 – £2,500 per m², yet you pay architects, engineers, and the council directly, so it pays to see each one as its own line. Professional fees are the price of getting the project designed, approved, and signed off correctly, which is money well spent when a mistake on the drawings costs far more to fix on site. See finding an architect for how to appoint the right professional and keep those fees under control.