Why a Flat 10% Contingency Fails: How to Size Your Rehab Buffer by Line Item, Property Age, and Scope

What Contingency Actually Covers (and Why 10% Is a Guess, Not a Rule)

Contingency is money reserved for unknowns inside the scope you already planned. If you budgeted to replace a bathroom subfloor and the rot turns out to run into two floor joists, that overage is contingency. It is not a fund for upgrading to quartz halfway through the job, and it is not a place to park items you knew about but never priced. Once those costs get mixed in, the buffer is gone before anything truly unexpected happens.

Keep four buckets separate in your budget: known line items, contingency for hidden conditions within those items, scope changes you choose to make, and holding costs like loan interest, taxes, insurance, and utilities. Each one has a different cause and a different fix. When an investor says they "blew through contingency," the real culprit is often a scope change or an extra month of carrying costs charged against the wrong bucket.

The flat 10% rule fails because it ignores where risk actually lives. On a $40,000 rehab, 10% is $4,000 no matter what the house looks like. A 1995 ranch getting paint, LVP, and new fixtures has very little hidden risk, so that $4,000 inflates your costs and can push your offer below what wins the deal. A 1940s house with original plumbing and wiring behind plaster can hide far more than $4,000 in surprises. The percentage is the same, but the errors point in opposite directions.

The better method is to assign a risk percentage to each line item based on how much of it you cannot see before closing. Visible, surface work gets a low rate. Anything behind walls, under floors, or underground gets a high one. Here is a quick example:

• Interior paint: $8,000 x 5% = $400
• Flooring (possible subfloor issues): $6,000 x 10% = $600
• Supply and drain plumbing behind walls: $10,000 x 25% = $2,500

That totals $3,500 on a $24,000 scope, a blended 14.6% contingency. You can defend that number line by line to a lender or partner, and it adjusts automatically as the risk mix of the job changes. The next two examples show how far this blended rate can swing from 10% in either direction.

Worked Example 1: A 1990s Cosmetic Flip Where 10% Is Too Much

Picture a 1994 three-bed ranch in a stable suburb with an ARV of $280,000 backed by recent comps. The scope is purely cosmetic: interior paint at $9,000, LVP flooring throughout at $11,000, new light and plumbing fixtures at $5,500, and a kitchen refresh (painted cabinets, new counters, new hardware) at $12,500. That totals a $38,000 rehab. Nothing in the plan opens a wall or touches the structure.

Apply an 8% contingency and you get $38,000 x 0.08 = $3,040, for a total rehab budget of $41,040. Your MAO becomes ($280,000 x 0.70) - $41,040 = $196,000 - $41,040 = $154,960. For comparison, a flat 10% buffer ($3,800) pushes the total to $41,800 and drops your MAO to $154,200. The gap looks small on one line, but it compounds when investors also pad every individual line item before adding contingency on top.

The smaller buffer is justified because this house carries low-visibility risk. A mid-1990s build predates neither modern wiring nor copper or PEX supply lines, so you are not budgeting for knob-and-tube or failing galvanized pipe. It was built well after the 1978 lead paint ban, and asbestos is unlikely in its finishes. Your realistic surprises are things like a subfloor soft spot under the old carpet or a countertop that costs more than quoted, which are cheap and quick to absorb.

Overpadding a deal like this has a real cost. If a competing buyer runs a tight 8% and you run 15% ($5,700), your MAO falls to $152,300, which is $2,660 below theirs. In a multiple-offer situation, that difference decides who gets the contract. Excess contingency does not make you safer when the risk is not there; it just makes you lose clean deals to investors who read the property more accurately.

The lesson is that contingency should track the uncertainty in the scope, not a habit. When the work is visible, finish-level, and on a younger house, a buffer in the 5% to 8% range protects you without pricing you out of the deal.

Worked Example 2: A 1940s House Where 10% Gets You Burned

Now consider the opposite case. You're looking at a 1946 bungalow with an ARV of $310,000 and a base rehab estimate of $72,000. The walls are plaster, the wiring is undocumented, and the drain lines are likely original cast iron or clay. A flat 10% adds $7,200 and calls it done, but the risk in this house isn't spread evenly across the budget. So assign each line its own contingency rate based on how likely it is to grow once the walls come open:

• Electrical: $14,000 at 30% = $4,200 (knob-and-tube or ungrounded circuits often force a full rewire)
• Plumbing: $11,000 at 30% = $3,300 (old supply and drain lines rarely stop where you planned)
• Roof: $9,000 at 15% = $1,350 (rotted decking shows up after tear-off)
• Cosmetic: $38,000 at 5% = $1,900 (paint, flooring, and fixtures are easy to quote and predictable)

That adds up to $10,750. Add a fixed $5,000 reserve for structural unknowns like sill plate rot, undersized joists, or a settled pier, and your total contingency is $15,750, roughly 22% of the base rehab. Notice that cosmetic work makes up more than half the budget yet contributes the least risk. The real exposure sits in the systems you can't see.

Run both versions through the 70% rule. First, $310,000 x 0.70 = $217,000. With a flat 10%, total repairs come to $79,200, so MAO = $217,000 - $79,200 = $137,800. With the risk-weighted buffer, total repairs are $87,750, so MAO = $217,000 - $87,750 = $129,250.

The gap is $8,550. If you offer $137,800 and the electrical and plumbing behave the way they usually do in a house this age, that $8,550 doesn't come from a cushion. It comes straight out of your profit, and on a tight deal it can turn a solid flip into a break-even. On older homes, the lower offer isn't timid. It's the number that actually reflects the house you're buying.

Adjusting Your Buffer: Inspections, Permits, Occupancy, and Who Holds the Money

Your line-item percentages are a starting point, and new information should move them. A $300 sewer scope showing a recently lined lateral lets you drop plumbing risk from 25% to 10%. A scope showing root intrusion in clay pipe means you price the replacement as its own line item and keep a smaller buffer on it. Inspections turn unknowns into known costs, and known costs need less cushion.

Homes you couldn't fully access push risk the other way. If the basement was locked, the attic hatch was painted shut, or you got fifteen minutes with a wholesaler, add 5 to 10 points to every system you didn't see. Permits work similarly. An electrical permit on an older house can trigger code upgrades like AFCI breakers, hardwired smoke and CO detectors, or a panel upgrade, so raise the electrical line rather than padding the whole budget.

Tenant-occupied properties hide damage behind furniture and clutter, and they add timing risk if the tenant leaves late. Add holding-cost padding plus extra cushion on flooring, drywall, and appliances you couldn't inspect. Contract structure matters too. A fixed bid shifts overrun risk to the contractor, so you can carry less on labor. Time-and-materials puts that risk back on you, so raise labor contingency by 10 points or more.

Keep contingency out of the contractor's draw schedule. On a $60,000 rehab with an $8,000 buffer, the contractor sees a $60,000 schedule. Approved, written change orders get paid from your contingency. If the contractor sees $68,000, scope tends to grow until it's spent.

Lenders handle contingency differently, so ask before you close. Many hard money lenders hold rehab funds back and release them in draws only after an inspector verifies completed work, and some require a contingency line in your budget. Unused contingency typically isn't paid out as cash. If your lender charges interest only on drawn funds, not drawing it saves money. If they charge on the full loan amount, you pay for that buffer whether you use it or not.

Contingency Mistakes That Quietly Erase Flip Profit

Most blown contingencies come from how investors spend the buffer, not how they size it. The most common leak is using it to fund upgrades you decided on mid-project. You open the kitchen, decide quartz beats laminate, swap the tub insert for a tile shower, and $4,000 of buffer is gone. Then the rotted subfloor shows up under that tub. Upgrades are scope changes, so give them their own line and justify them against ARV.

The second mistake is applying your percentage only to cosmetic costs. Say your budget is $25,000 in paint, flooring, and kitchen plus $15,000 for a roof and electrical panel. Taking 10% of the $25,000 gives you $2,500, but your riskiest dollars sit in the $15,000 of systems work. The third mistake is ignoring time. A three-week delay on a house costing $1,800 a month to hold (interest, taxes, insurance, utilities) adds about $1,350 that never appears in the rehab budget.

The fourth mistake is double-counting. A contractor bids $8,000 for a bathroom, you pad it to $9,500, then add 15% contingency on top. Repeat that across five lines and your repair number swells, your MAO shrinks, and you lose deals you should have won. The fifth mistake runs the other way: dropping the buffer to make a deal pencil. Take a $240,000 ARV: $168,000 minus $40,000 in repairs and $6,000 in contingency gives a $122,000 MAO. If the seller wants $127,000 and you cut contingency to $1,000 to match, you have not found a deal. You have just hidden the risk.

The fix is to see your budget line by line before you set any buffer. Paste the address into FlipSmrt and the line-item rehab budget separates systems work from cosmetic work. You can then assign 20 to 25% to roof, plumbing, and electrical and around 5% to paint and fixtures. On the $40,000 example, that weighted approach puts the buffer where the surprises actually live.

Rehab Contingency FAQ

Should contingency go into your MAO math? Yes. Treat it as part of your repair costs, not a separate cushion you hope never to touch. Say ARV is $300,000, your line-item rehab is $45,000, and you carry a $6,000 contingency. Your MAO is ($300,000 x 0.70) - $51,000 = $159,000. Leave contingency out and you would offer $165,000, so every surprise comes straight out of your profit.

What percentage is reasonable for a full gut? A full gut exposes everything behind the walls, so 15% to 20% of the line-item budget is a sensible starting range. Push toward 20% or higher when the house predates 1960 or the inspection flagged wiring, plumbing, or foundation concerns. On a $90,000 gut, that means holding $13,500 to $18,000 in reserve. If that number kills the deal, the deal was thinner than it looked.

Does a newer roof or HVAC lower the buffer? It lowers the buffer for those specific line items, not for the whole project. A documented three-year-old roof can carry close to zero roof contingency. A new furnace does nothing to reduce the risk of rotted subfloor or galvanized supply lines, though. Ask for receipts, permits, or warranty paperwork before you trim anything, because "the seller said it's new" is not documentation.

Should you disclose contingency to contractors? Generally, no. When a contractor knows you have $10,000 set aside, change orders have a way of growing to fill it. Get a fixed bid on a clearly written scope, and require written change orders with pricing approved before any extra work starts. Your contingency is your risk reserve, not part of their budget.

What do you do with leftover contingency? Resist the urge to spend it on upgrades that won't move ARV, like premium fixtures in a mid-range neighborhood. Let it fall to profit, pay down your loan to cut holding costs, or carry it into reserves for the next project. Then compare actual versus estimated cost on each line item so your next contingency is based on your own data instead of a guess.