Every renovation budget is really two numbers. The first is the quote you'll hold in your hand — a price for a defined scope, prepared by a contractor who hasn't opened your walls yet. The second is what the project will actually cost, and the difference between them is where most budgets break. The contingency is your buffer for that gap, and unlike almost everything else in a renovation, it's the one part entirely under your control: you set its size, you set the rules for spending it, and you decide when it's done.

This guide walks through what a contingency should and shouldn't cover, how big it needs to be for your specific house and scope, and which stages of work are most likely to draw on it.

What a contingency is for — and what it isn't

A contingency exists for one category of money: costs that are real but not yet visible. Opening a floor that turns out to be uneven under the tiles. An electrical circuit that fails inspection and needs replacing, not patching. Drainage that was "fine" until the landscaping equipment crossed it. These aren't extras in any meaningful sense — they're part of the job — but no honest contractor can quote what nobody has seen yet.

Just as important is what a contingency is not for:

  • Upgrades and wants. The better faucet, the stone instead of laminate, the additional cabinet. If a cost exists because you chose it, it's a budget decision, not a contingency draw. Blurring this line is the single most common way reserves quietly vanish — scope creep deserves its own discipline, funded separately.
  • Known variable costs. If the quote includes an allowance for tiles because you haven't picked them yet, reconciling that allowance against your eventual choice is ordinary quote mechanics — not a contingency event (more on this below).
  • The contractor's mistakes. If a contractor damages something or misprices their own scope, that's theirs to resolve. Your contingency funds the house's unknowns, not anyone's errors.

Contingency vs. the allowances already in your quote

These two get confused constantly, and the confusion makes budgets look more complete than they are.

An allowance is a provisional amount inside the quote for something the project definitely requires but that hasn't been specified yet — a figure per square meter for tiles, a lump sum for light fixtures. When you choose the actual item, the allowance is reconciled: choose cheaper and the quote drops; choose dearer and you pay the difference. Allowances get consumed by your decisions.

A contingency sits outside the quote entirely and is held by you, for conditions nobody knows about yet. It doesn't shrink because you chose a cheaper faucet, and it doesn't get consumed by decisions at all.

Both belong in a healthy budget. A quote full of allowances isn't padded — it's honest about what's undecided. But allowances and contingencies answer different questions, and replacing one with the other is how a project ends up "fully funded" on paper while having no actual reserve.

How much to hold back above the quote

There's no single number — but there is a commonly used rule of thumb with a well-defined shape. Guides on both sides of the Atlantic typically advise holding 10–20% of the project cost, and the position within (or above) that range is driven by two variables:

The age of the house. The older the property, the more likely it is that opening walls and floors reveals end-of-life systems or legacy materials that must be handled — the dynamic behind hidden renovation costs in old houses. A pre-war house that hasn't been touched in decades sits at the top of the range or beyond it; many old-house guides advise 20% or more for exactly this reason. A 2010s build with modern systems needs far less headroom.

The depth of the work. Cosmetic scope — replacing finishes in place, nothing opened — has almost nothing to discover, and the low end of the range is realistic. Full remodels that open walls, move plumbing or touch structure are where discoveries live, so the reserve should sit higher.

A practical way to size it: start at 10% for genuinely cosmetic work on a newer home; move toward 15% as scope starts opening walls; move to 20% or above for full remodels in older homes. If your project mixes both — a modern extension off a Victorian shell — split the reserve by scope rather than applying one percentage to everything. Phasing decisions matter here too: work spread across phases carries discovery risk in each phase, and reopening closed-up areas is among the most expensive ways to spend a contingency.

One caution: treat any precise figure you're given — including this guide's — as a starting point for your own risk assessment, not an answer. The right number depends on what your specific house hides, and the best-available estimate of that is a stage-by-stage look at what your scope actually touches.

Which stages actually eat the contingency

Contingency risk isn't spread evenly across a renovation — it's concentrated in the stages that open the building's fabric:

  • Demolition and prep — first in line. Everything concealed behind surfaces becomes visible here, which is why discoveries typically announce themselves in week one even though their costs land later.
  • Electrical — legacy wiring, undersized panels, and circuits that fail modern requirements once disturbed. Licensed trade labor makes every discovery expensive per hour.
  • Plumbing — corroded supply lines, tired drains, and hidden leaks are classic mid-project finds, and they often damage whatever they've been quietly leaking onto.
  • Walls and paint — opening a wall reveals what the last century of building practice left behind; closing it again after unplanned work costs a second time.
  • Ceiling — same exposure from above: legacy coatings, tired plaster, and anything the cavity above has been hiding.
  • Flooring — uneven or damaged subfloors surface the moment old coverings come up.
  • Fixtures and finishes — almost no discovery risk. By this stage, either the unknowns have surfaced or they haven't.

The pattern is the mirror image of the cost-comparison pattern: finishes carry the budget's biggest choices, but structure and systems carry its biggest unknowns. A contingency that's sized by looking at a quote's biggest line items is usually sized wrong — the biggest line item (finishes) is often the safest.

Running the reserve well

Size is half the discipline; handling is the other half. Four practices separate reserves that survive a project from reserves that evaporate:

  1. Hold it separately and mentally label it. Not a line in the quote, not part of the deposit conversation. A distinct pot that exists for one purpose.
  2. Write the trigger rule before work starts. One sentence, agreed with yourself (and ideally with your contractor): contingency draws require a documented unforeseen condition, a stated price, and no cheaper alternative that meets the requirement. The rule protects the reserve from the project's most dangerous phase — the middle, where everything feels urgent.
  3. Log every draw. Amount, cause, and the stage it hit. By the end you'll know whether your reserve was sized right — knowledge that makes the next project's budget dramatically better.
  4. Release what's left deliberately. After snagging is closed, remaining contingency is freed money — window treatments, furniture, or savings. Decide where it goes rather than letting it dissolve into general spending.

If you want a stage-by-stage picture of what your specific project involves — the starting point for sizing a reserve that matches your house rather than an average one — RenoPlan's calculator builds it from your description and market rate data, with labor and materials broken down per stage. It's a planning range, not a quote, and paired with a right-sized contingency it gives you a budget that survives contact with your actual walls.

Frequently Asked Questions

Is a 10% contingency enough?
For cosmetic work on a newer home, 10% is often enough. It starts to look thin as the work gets deeper or the house gets older: guides commonly advise 10–20% as the working range, with full remodels and older homes at the top of that range or above it, because that's where opening walls tends to reveal work nobody could price in advance.
Should the contingency be part of the contractor's quote?
No — it's your reserve, held outside the contract. A contingency inside the quote just inflates every line item. What should be in the quote is the contractor's own handling of unknowns: stated allowances for things not yet chosen, and a written policy for concealed conditions. The contingency you hold personally sits on top of that.
What happens if I don't use the contingency?
Nothing dramatic — it's still your money. Once the work is done and the snagging list is closed, whatever's left of the reserve is released: it can fund the furniture and window treatments the renovation always seems to demand, or simply roll into savings. Not spending the contingency is the normal outcome of a well-scoped project, not a sign you budgeted wrong.
What's the difference between a contingency and a contractor's allowance?
An allowance is inside the quote: a provisional sum for something the project definitely needs but that hasn't been chosen yet — say, a fixed amount for tiles — which is later reconciled against your actual selection. A contingency sits outside the quote entirely and covers things nobody knows are needed yet. Confusing the two is how budgets look fully funded when they aren't: allowances get consumed by decisions, not by surprises.