Start with two numbers, not one

Before you lift a single floorboard, write down two figures. The first is the amount you would love to spend. The second is the amount you can genuinely afford without touching money you will need in the next year. Most British renovation projects land somewhere between 15% and 25% above that first, hopeful figure — and the gap between the two numbers is where all the stress lives.

Be honest about what you are taking on. A straightforward bathroom refresh in a 1970s semi is a very different beast from a kitchen-diner extension in a Victorian terrace. The older the house, the more likely you are to find something nobody planned for. Budget for the house you actually own, not the one in the magazine.

Set a contingency you will not raid

A contingency is not spare cash, and it is not your decorating budget. It is a separate line that exists purely to absorb surprises. Treat it as untouchable until the job is finished and snagged.

• 10% for straightforward cosmetic work, such as decorating, replacing flooring or a like-for-like kitchen swap.
• 15% once plumbing, electrics or a wall comes out of the equation.
• 20% or more for period properties, anything pre-1930, or where the walls have not yet been opened up.

The usual culprits are depressingly predictable: asbestos in old floor tiles or artex ceilings, wiring that predates the last three sets of regulations, wet rot under a leaking shower, a missing lintel above an opening, or a drain that runs exactly where you wanted the new soil pipe. None of these are exotic. All of them are expensive. A healthy contingency turns a catastrophe into an inconvenience.

Gather three quotes, then compare them properly

Three written quotes is the minimum, and they must be for the same scope of work. A quote that looks cheapest often is not, because something has been quietly left out.

• Ask specifically what is excluded: skip hire, waste removal, making good after plastering, VAT, decorating, and the final clean.
• Check whether the price includes materials at a fixed rate or is subject to "plus materials", which can drift badly.
• Ask how many weeks the job will take and who will actually be on site each day — the person quoting is not always the person tiling.
• Request two recent references and, ideally, one address you can visit.
• Confirm insurance, and for gas or electrical work, that the relevant registered engineer will sign it off.

Then set the quotes side by side and compare the middle figure, not the lowest. A price that is 20% under the others usually means something is missing, not that you have found a bargain.

Track spending every single week

This is the habit that saves the most money, and it takes fifteen minutes. Set up one simple spreadsheet with columns for date, item, supplier, estimated cost, actual cost and running total. Every Friday, sit down with your receipts and update it.

Two things happen when you do this. First, you spot overspend while there is still time to correct it — a fortnight of small merchant trips can quietly add £600 to a project. Second, you stop relying on memory, which is always optimistic. Keep a dedicated folder, physical or on your phone, for every receipt and invoice.

Crucially, any change to the agreed work — a variation — should be written down and priced before the trade starts it. A quick text saying "yes, go ahead" is how budgets disappear.

Stage your payments and hold a retention

Never pay a large lump sum up front. A modest deposit to cover materials is reasonable; handing over half the job's value before any work begins is not. Agree a payment schedule tied to milestones instead — first fix complete, plastering done, second fix complete — and pay as each is reached.

Hold back a retention of around 5% until snagging is finished. It is a small sum that gives you real leverage if a wobbly door or a dripping tap is left unresolved. Keep everything in writing, even if it is just a clear email summarising what was agreed, and never pay in cash without a receipt.

Know where to save and where not to

There is plenty of room to trim a budget without wrecking the finish.

• Save on: paint, tiling, your own labour for stripping out and demolition, seconds and end-of-line tiles, reusing sound kitchen carcasses with new doors, and hiring a van to take waste to the tip instead of a skip.
• Do not save on: electrics, gas, structural work, damp proofing, tanking, the boiler, or windows and doors. These are the things that are buried, certified or weather-facing, and correcting them later costs multiples of doing them properly first time.

Reconsidering the layout is often the cheapest way to save thousands, because moving a soil pipe or a radiator is where labour really piles up. Keep the sink, the cooker and the bathroom where they are, and spend the money on things you will touch and see every day: worktops, taps, handles and lighting.