Window and Door Budget Calculator

A window and door package is one of the largest single orders in an extension budget. A medium three-panel aluminium bifold set typically runs £3,150 – £4,670 supplied and installed, and each medium opening aluminium casement window adds £600 – £1,100. This estimator adds those together for your own mix of frames, so you can sanity-check a glazing quote before you commit to a deposit.

Enter how many windows you need, pick a size and frame material, choose bifold or sliding doors, and the calculator builds a realistic budget for the whole windows and doors package. It reads current market rates for each combination rather than a single average, so the number moves as your specification does.

What drives the cost

Frame material is the biggest lever. Aluminium is the standard choice for modern extensions, with a slim frame and a built-in thermal break. uPVC is the budget option at £450 – £700 per medium window against £600 – £1,100 for aluminium, though the frames are noticeably thicker. Timber is the premium pick at £1,000 – £1,500 and needs re-treating every few years.

Opening style matters too. A fixed picture window with no opener is cheaper than a casement: a medium uPVC fixed pane is about £250 – £350 against £450 – £700 for the opening version. You still need at least one opening window per habitable room to meet Part L and fire escape rules, and a trickle vent for background ventilation, so most schedules mix fixed and opening frames.

The bespoke tier is aluminium only and roughly doubles the rate. A bespoke medium casement from a brand like Origin or Schuco lands at £1,600 – £2,600, and a wide bespoke bifold at £8,000 – £18,000. Integrated blinds, sealed inside the glass, add £3,500 – £7,000 to a door order.

Lead times and protecting your deposit

Glazing is a made-to-order product, so the lead time is the part that catches people out. Standard aluminium frames take eight to twelve weeks, and bespoke systems stretch to sixteen in peak season. A good window installer will survey the opening only after the steel is in and the walls are up, then manufacture, so order early and build the wait into your programme.

Always pay at least part of a door deposit on a credit card. Under Section 75 of the Consumer Credit Act your card provider is jointly liable if the supplier fails to deliver, and a single card payment on a large order buys that protection cheaply.

A worked example

Take a typical single-storey rear extension: four medium opening aluminium casement windows at £600 – £1,100 each, plus one medium three-panel aluminium bifold at £3,150 – £4,670. Add a small allowance per frame for sealing and weatherproofing, and the calculator returns the combined range above.

Switch the doors to a sliding set at £2,500 – £3,500 and the figure barely moves; switch the whole order to the bespoke aluminium tier and it roughly doubles. That is the value of pricing your own mix rather than trusting a single headline rate: the specification you choose, not the floor area, sets this budget.