By the Home Savings Calculator team · 29 August 2026 · 6 min read
A single lump-sum guess hides which half is moving. Materials you control by choosing differently; labour you control by changing the scope or the schedule. A budget that does not separate them cannot be adjusted intelligently when it comes in high.
On decorating and flooring, labour is frequently the larger half. That surprises people who spent their planning time choosing paint.
Run the room through the renovation cost calculator and look at the materials versus labour split before you choose anything. It reframes where your decisions actually matter.
Wall area is the room perimeter multiplied by ceiling height. Floor area is length times width, measured at the widest points, with alcoves added separately. Both take five minutes and remove most of the guesswork from every figure that follows.
Most people do not subtract doors and windows from wall area. Leaving them in builds a little slack, which is generally welcome by the second coat.
Every material cut to fit a room generates offcuts. Ten percent extra is standard for straight-laid flooring and tiling, fifteen for diagonal or herringbone layouts, and more for patterned tiles that have to align.
Order it all in one go. Dye lots and batches vary, and a top-up ordered three weeks later frequently does not match what is already down.
Preparation is the usual gap: filling, sanding, masking, dust sheets, moving furniture. Then waste removal, which on a floor replacement can be a skip on its own. Then the trade's margin, which is not padding either — it is how the business survives a job that goes wrong.
This is why a calculator figure and a quote differ, and why the difference is not evidence of being overcharged. Use the estimate to interrogate a quote, not to argue with it.
Ten percent on a cosmetic job, twenty on anything that opens up a wall or a floor. Older properties reliably hide something: a damp patch, a floor that is not level, wiring that should not still be there.
A contingency you do not spend is a good outcome. A budget with no contingency is not a budget, it is a hope.
