Make vs. Buy: The Avoidable-Cost Framework Behind Every Smart Outsourcing Decision

A supplier just quoted you $12 a unit for a part your cost sheets say costs $15 to make in-house. The math looks obvious — sign the purchase order and pocket the 20 percent savings. But that $15 is almost certainly lying to you. It bundles in warehouse rent, equipment depreciation, and a slice of the plant manager's salary, and not one of those bills disappears when you outsource. Compare the supplier's price against the costs you can actually shed, and the "obvious" decision frequently flips.

This is the make-or-buy decision, and small businesses face it constantly: manufacture the component or purchase it, hire the bookkeeper or outsource the books, build the software tool or subscribe to one. About 37 percent of small businesses already outsource at least one core function such as accounting or IT, and most of the rest will confront the same choice as they grow. The framework below shows you which costs belong in the comparison, how to run the math, and which non-financial questions can override it.

The Only Costs That Matter Are the Ones You Can Avoid​

The single biggest error in make-or-buy analysis is comparing the supplier's quoted price against your fully loaded in-house unit cost. That in-house number typically includes allocated fixed overhead — rent, insurance, salaried supervision, depreciation — that stays put whether you make or buy. Those are unavoidable costs, and including them rigs the comparison in favor of outsourcing.

Instead, sort every in-house cost into one of three buckets:

• Avoidable costs — count them. Direct materials, direct labor, and variable overhead disappear if you stop producing. So do fixed costs tied specifically to the activity, such as a supervisor who would be reassigned or let go, or a leased machine you would return. These are the relevant costs of making.
• Unavoidable costs — ignore them. Allocated corporate overhead, depreciation on equipment you already own, and rent on space you will keep paying for remain either way. They are irrelevant to the decision.
• Sunk costs — ignore them completely. Money already spent, such as the purchase price of existing equipment or past R&D, cannot be recovered and must never enter the comparison.

Accounting practitioners put the rule bluntly: only direct, out-of-pocket costs belong on the "make" side of the ledger. Everything else is noise that makes outsourcing look cheaper than it is — or, when the fixed costs genuinely would go away, makes in-house production look cheaper than it is. Honesty in this sorting step is the whole game.

Running the Math: A Worked Example​

Suppose your shop makes 10,000 units a year of a component with the following cost structure per unit:

A supplier offers the identical component at $15.00 per unit, delivered. Against the $18.00 full cost, buying looks like a $3.00-per-unit win — $30,000 a year. Against the $14.00 avoidable cost, making wins by $1.00 a unit, or $10,000 a year. The $4.00 of unavoidable fixed overhead per unit stays on your books either way; outsourcing just spreads it over fewer units and makes everything else you produce look more expensive.

Now add the wrinkle that decides many real cases: opportunity cost. Suppose the freed-up floor space and labor could take on a rush job netting $25,000 a year. That forgone profit is a genuine cost of continuing to make. The comparison becomes $14.00 × 10,000 + $25,000 = $165,000 to make versus $15.00 × 10,000 = $150,000 to buy — and buying wins. Opportunity cost belongs in the analysis whenever idle capacity has a valuable alternative use, and it is the item owners most often forget.

The Buy Side Has Hidden Costs Too​

So far the supplier's $15.00 quote has been taken at face value. Do not. The true cost of buying — its total cost of ownership — runs well beyond the purchase price. Before you compare, add:

• Freight, sales tax, and duties on incoming goods.
• Ordering and receiving costs: purchase orders, inspections, and the staff time to manage the supplier relationship.
• Inventory holding costs: warehousing, handling, insurance, and the cash tied up in safety stock you would not need if you produced just in time.
• Quality failure costs: rework, scrap, returns, and warranty claims when a supplier's defect rate exceeds yours.
• Stockout and switching risk: the cost of late deliveries, plus the switching expense if the relationship fails and you must re-source or rebuild in-house capability.

In practice, these add 10 to 25 percent on top of the quoted price for many small manufacturers, and they are the reason a quote that beats your avoidable cost on paper can still lose in reality. Ask the supplier for delivered, inspected, ready-to-use cost — not ex-works price — and estimate the rest from your own receiving and quality records.

The Capacity Question Cuts Both Ways​

Capacity is where textbook analysis meets shop-floor reality, and it pushes in both directions depending on your situation.

If you have idle capacity, making is cheap at the margin. The equipment, space, and salaried staff are already paid for, so the incremental cost of producing one more unit is just materials, piece-rate labor, and variable overhead. Buying while machines sit idle means paying twice: once for the capacity you own and again for the supplier's.

If you are at or near capacity, making has a hidden price: every unit of the component displaces other profitable work. That displaced contribution margin is an opportunity cost of making, exactly as in the worked example above. Outsourcing the component can also relieve a bottleneck operation — if your constraint is machine hours on one overloaded work center, shifting work to a supplier frees the bottleneck to produce more of what only you can make. But if the bottleneck is elsewhere, say in sales rather than production, that argument evaporates.

On the supplier side, ask the mirror question: will you get capacity when it matters? A small buyer can be a rounding error in a large supplier's order book, which means minimal deliveries during high-demand periods. Reliability of supply is a capacity question too, and a cheaper price that comes with allocation risk is not cheaper.

The Qualitative Factors That Can Override the Math​

A rigorous make-or-buy analysis often ends with the numbers pointing one way and judgment pointing the other. The following factors legitimately overrule a spreadsheet:

• Expertise and quality. If your in-house defect rate is high and you lack the skills or equipment to fix it, outsourcing to a specialist may be the only path to acceptable quality. Conversely, if quality is your differentiator, handing the process to a vendor surrenders control over what customers pay you for.
• Strategic importance. Components core to your competitive advantage — proprietary formulations, signature processes, technology you do not want a supplier to learn — should generally stay in-house even when buying is cheaper. Commodity inputs with no strategic weight are the natural outsourced candidates.
• Funding and equipment. In-house production can demand capital you do not have. For cash-constrained startups, avoiding an equipment purchase is often decisive. Running the other direction, outsourcing can free cash if you can sell equipment you no longer need.
• Flexibility and demand volatility. Suppliers absorb volume swings more cheaply than you can when demand is spiky: you order more or less instead of hiring, laying off, or carrying idle equipment. But when demand is stable and predictable, that flexibility premium buys you nothing.
• Working capital. Some suppliers will warehouse goods and drop-ship directly to your customers, shifting inventory investment off your balance sheet — a substantial working capital saving. The trade-off is that the supplier learns who your customers are.
• Speed and control. In-house production gives you priority, customization, and fast iteration. Outsourcing inserts lead times, minimum order quantities, and a queue you do not control.

None of these appears in the avoidable-cost comparison, yet any one of them can dominate it. The right process is quantitative first, qualitative second: run the numbers honestly, then ask whether the non-financial factors are strong enough to change the answer — and write down why, so next year's review starts from reasoning rather than memory.

Mistakes That Routinely Wreck the Analysis​

Even owners who know the framework stumble on the same handful of errors:

1. Loading in-house cost with allocated overhead. The classic mistake, and it always favors buying. If the plant manager's salary does not change with your decision, it does not belong in your decision.
2. Counting sunk costs as costs of making. The machine is bought and paid for; its depreciation is not a reason to outsource.
3. Ignoring opportunity cost. Idle capacity with no alternative use argues for making; capacity that could earn money elsewhere argues for buying. Both directions get forgotten.
4. Comparing against the sticker price. The supplier's quote without freight, inspection, inventory carrying cost, and management time understates buying by a wide margin.
5. Treating a one-time quote as permanent. Supplier prices rise, quality drifts, and lead times stretch. Build the contract terms — price locks, quality standards, exit clauses — into the decision, and calendar a re-analysis at least annually.
6. Deciding once and never revisiting. Volumes change, capacity fills, suppliers get acquired. A make decision at 5,000 units can become a buy decision at 50,000 when the supplier's economies of scale kick in — or the reverse when your own scale arrives.

A Decision Checklist You Can Reuse​

For each make-or-buy choice, work through these steps in order and keep the worksheet — it is next year's starting point:

1. Define exactly what "make" includes: which component, what volume, over what time horizon.
2. List every in-house cost and mark each avoidable, unavoidable, or sunk. Total only the avoidable ones.
3. Get the supplier's all-in quote: price plus freight, tax, inspection, and onboarding costs.
4. Estimate ongoing buy-side costs: inventory carrying, ordering, quality failures, and supplier management.
5. Price the opportunity cost of capacity in both directions: idle capacity favors making; displaced work favors buying.
6. Compare totals, then stress-test: what volume change, price increase, or quality slip flips the answer?
7. Apply the qualitative screen — expertise, strategy, funding, flexibility, working capital — and record any override with its reason.
8. Set a review date. Annual is the minimum; tie it to contract renewals and budget season.

You Cannot Run This Analysis on Messy Books​

Notice how every step above demands cost data most small businesses do not have at their fingertips: direct labor separated from supervision, variable overhead isolated from fixed, receiving and inspection costs tracked per product line. When those figures live in one undivided "cost of goods sold" bucket, the avoidable-cost sort becomes guesswork — and guesswork systematically favors whichever option the owner already prefers.

The fix is structural, not heroic. Track direct materials, direct labor, and variable overhead in distinct accounts, keep allocated overhead visibly separate from incremental spending, and reconcile supplier-related costs — freight in, inspection labor, inventory carrying charges — where you can find them. The Beancount documentation walks through setting up that kind of granular, auditable cost tracking. A make-or-buy worksheet fed by clean ledgers takes an afternoon; the same worksheet fed by tangled books takes a month and still misleads.

Keep Your Outsourcing Decisions Grounded in Real Numbers​

Every outsourcing choice is really a bookkeeping choice first: without trustworthy cost data, you are comparing a precise supplier quote against a vague in-house guess. Beancount.io provides plain-text accounting that gives you complete transparency and control over your financial data — no black boxes, no vendor lock-in. Get started for free and run your next make-or-buy decision on numbers you can defend.