AISC Explained: The Mining Cost Metric That Shows Who Survives a Downturn

All-in sustaining cost (AISC) is the number that shows which gold and base-metal producers can keep operating when the metal price rolls over. This guide breaks down what AISC captures beyond simple cash cost, how the industry cost curve works, and how to read a producer's AISC margin and breakeven price.

What AISC actually measures

All-in sustaining cost (AISC) is the mining industry's answer to a simple question: what does it really cost to keep an ounce of gold (or a pound of copper) coming out of the ground, year after year, without the mine quietly falling apart? It was formalised by the World Gold Council in 2013 because the older headline figure — "cash cost" — flattered producers by ignoring the capital a mine must keep spending just to stand still. AISC is a non-GAAP guideline, not an accounting standard, so companies apply it with some discretion. That discretion is exactly why an investor has to understand how the number is built before comparing one producer to another.

The intuition is survival. A mine that spends nothing on new haul trucks, tailings-dam lifts, or underground development posts a low cash cost this year and then grinds to a halt in three. AISC folds that "keep-the-lights-on" capital back in, so it approximates the price a metal must fetch for the operation to be self-sustaining. When investors call AISC the survival metric, this is what they mean: below it, an operation is consuming itself rather than funding itself.

The cost stack: from C1 cash cost to AISC

AISC is best understood as a stack. You start at the rock face and add layers until you reach the number reported to shareholders. The table below walks an illustrative gold operation from the direct cost of moving and treating ore all the way up to AISC. Every figure is illustrative and expressed per troy ounce; real operations vary widely.

Two things are worth noticing. First, on-site G&A sits inside cash cost, while the corporate G&A added at the AISC stage is the head-office slice attributed to that operation — they are different lines, not double-counting. Second, the jump from a $950 cash cost to a $1,300 AISC is $350 per ounce, roughly 37%. That gap is the part of the cost base that pure cash-cost reporting hides, and it is the difference between a mine that looks cheap and a mine that is actually self-funding.

C1 cash cost vs AISC vs AIC

Three cost figures dominate mining disclosure, and they are not interchangeable. Reading a producer's release without knowing which one is quoted is a common source of confusion.

The step from AISC to AIC is the one investors most often overlook. AISC deliberately excludes the capital spent to expand — a new decline, a mill expansion, a greenfield build. AIC adds that back. So a company can report a comfortable AISC while its AIC, and its actual cash flow, are deeply negative because it is pouring money into a growth project. In our illustrative mine, adding $250/oz of expansion capital lifts AIC to roughly $1,550/oz even though AISC stays at $1,300. Neither figure includes interest or income tax, which is why even AIC is not the same as free cash flow.

Reading the cost curve: four producers, two prices

Rank every operating mine from cheapest to most expensive and you get the industry cost curve. The first quartile (lowest-cost 25% of output) survives almost any downturn; the fourth quartile is marginal and is cut first when prices fall. Because demand has to be met by someone, the metal price tends to gravitate toward the cost of the highest-cost producer still needed to supply the market — the marginal cost. The table ranks four illustrative gold producers and shows their AISC margin at two gold prices.

At an illustrative $1,700/oz, Producer D is under water — losing roughly $250 an ounce on an all-in sustaining basis — while Producer C is barely breathing at a 6% margin. At $2,300/oz all four are profitable, and the gap between them compresses in percentage terms even as the low-cost producer keeps the widest dollar margin. That is the whole point of curve position: the first-quartile miner is comfortable across a wide band of prices, while the fourth-quartile miner's fate swings entirely on the metal price. Position on the curve, not any single quarter's AISC, is what determines who endures a downturn.

AISC margin and the breakeven price

AISC margin is deliberately simple: the realised metal price minus AISC. As a percentage it is (price − AISC) ÷ price. For Producer B at $2,000/oz, that is (2,000 − 1,300) ÷ 2,000 = 35%. The breakeven price is just the point where that margin is zero — the price equal to AISC. Producer B breaks even at $1,300/oz on a sustaining basis; below it, the operation is not covering the capital it needs to keep running.

Because AISC excludes growth capital, financing and tax, breakeven on AISC is a floor for sustaining the mine, not for funding the whole company. A producer building a second mine can sit above its AISC breakeven and still burn cash overall. Investors often treat the AISC breakeven as one input among many — a measure of operational resilience — rather than a complete picture of solvency.

Why by-product and co-product accounting change the number

Few gold mines produce only gold. Many yield silver, copper or zinc alongside it, and how a company treats that secondary metal can swing reported AISC dramatically. Under the by-product method, revenue from the secondary metal is credited against costs, lowering the reported cost per gold ounce. A gold mine with a rich copper by-product can post an unusually low — occasionally even negative — gold AISC, simply because copper sales more than cover the residual cash cost. Under the co-product method, total costs are split between the metals in proportion to the revenue each contributes, so gold carries only its share and its per-ounce cost looks higher.

Neither method is wrong, but they are not comparable. Two mines with identical economics can report very different gold AISC purely because one nets out copper as a credit and the other allocates cost across both metals. The by-product figure also depends on the assumed price of the secondary metal — a higher copper assumption produces a larger credit and a lower headline gold AISC. The data behind the number matters as much as the number itself.

What moves the whole curve: input costs

Curve position is relative, but the curve itself is not fixed — it rises and falls with input costs that hit every producer at once. The biggest movers are energy and labour. Diesel powers haul fleets; electricity (grid, diesel gensets or hydro) drives grinding mills, which are among the most energy-hungry machines in industry. When fuel and power prices climb, the entire curve shifts upward, lifting the marginal cost and squeezing margins for everyone — the low-cost producer simply has more cushion to absorb it.

Labour is the other structural driver: skilled miners in remote districts command rising wages that feed straight into cash cost. Consumables matter too — grinding media and mill liners track steel, explosives track ammonium nitrate and natural gas, and cyanide and reagents track chemical markets. A broad bout of input-cost inflation can add hundreds of dollars per ounce across the sector, one reason industry-average gold AISC has drifted materially higher in recent years even at steady production volumes.

What sets a mine's place on the curve: grade and jurisdiction

Two levers explain most of the spread between first- and fourth-quartile producers. The first is ore grade — grams of gold per tonne of rock. Because the cost of mining and milling a tonne is broadly similar whether the tonne is rich or poor, higher grade spreads that fixed effort over more metal and drives unit cost down. A 5 g/t deposit can be structurally cheaper per ounce than a 1 g/t deposit even before anything else is considered. Related physical factors — strip ratio (waste moved per tonne of ore) in open pits, and depth, haulage distance and ventilation load underground — push in the same direction. Ageing mines that chase ore deeper tend to migrate up the curve over time.

The second lever is jurisdiction. Labour rates, the cost and source of power, royalty and tax regimes, infrastructure and permitting vary enormously by country and even by state or province. A mine on cheap hydro power with a low royalty and good roads starts with a structural advantage over an identical orebody reliant on trucked diesel and facing a high net-smelter-return royalty. Grade and jurisdiction together are why two mines producing the same metal can sit hundreds of dollars per ounce apart on one curve.

Common mistakes and edge cases

• Comparing AISC without checking the accounting method. A by-product gold AISC and a co-product gold AISC are not like-for-like. A copper-rich miner can show a far lower — even negative — gold AISC that reflects credit accounting, not superior operations.
• Reading AISC as cash flow. AISC excludes growth capital, financing, working capital and income tax. A producer can post a healthy AISC margin and still burn cash overall while building a new mine — which is exactly what AIC is designed to reveal.
• Assuming AISC is standardised. It is a non-GAAP guideline. What counts as "sustaining" versus "growth" capital involves judgment, and companies draw that line differently, which shifts the reported figure.
• Judging one asset by company-wide AISC. A blended corporate AISC can hide a fourth-quartile mine that is under water beneath the average of profitable ones. Asset-level disclosure tells a different story than the group headline.
• Over-reading a single quarter. AISC swings with the timing of sustaining capital and with grade sequencing — mining through a planned low-grade zone temporarily spikes cost per ounce. A one-quarter jump is often scheduling, not deterioration. Reclamation is a related trap: AISC captures the sustaining accretion of the closure liability, but the bulk of closure cash lands at end of mine life, so AISC understates that final outflow.

FAQ

What is a good AISC?

"Good" is relative to the metal price and to peers, not an absolute number. What matters is the AISC margin — the gap between the prevailing price and the cost — and where a producer sits on the industry cost curve. A first-quartile operation with a wide margin is resilient across a broad range of prices; a fourth-quartile one is exposed even if its raw AISC looks acceptable in a strong price environment.

What is the difference between AISC and cash cost?

Cash cost (C1) captures only direct site operating costs, net of by-product credits. AISC adds the layers a mine cannot skip if it wants to keep producing: royalties and production taxes, sustaining capital, corporate G&A and reclamation. AISC is typically a few hundred dollars per ounce above cash cost, and that gap is the cost that cash-cost reporting leaves out.

Why do miners report different AISC for similar operations?

Because AISC is a non-GAAP guideline applied with discretion. Differences in by-product versus co-product accounting, the assumed price of secondary metals, and where each company draws the sustaining-versus-growth capital line can all move the number, even for two economically similar mines.

What happens when the metal price falls below AISC?

Below AISC, an operation is not covering the capital it needs to sustain itself — it is effectively consuming the mine to keep selling metal. Producers in that position are usually the marginal, high-cost operations, and sustained sub-AISC prices are what historically prompt curtailments, care-and-maintenance decisions and supply cuts across the sector.

Does AISC include growth capital expenditure?

No. AISC deliberately excludes expansion and new-project (growth) capital. That spending is captured by all-in cost (AIC), which sits above AISC. This is why a company can report a solid AISC yet have negative overall cash flow while funding a major build.

Can AISC be negative?

Yes, though it is unusual. Under by-product accounting, if revenue from secondary metals such as copper or silver exceeds the residual cash cost and sustaining outlays, the reported AISC for the primary metal can turn negative. It reflects credit accounting on a polymetallic orebody rather than costless production.

How Quintarthai helps

Quintarthai is a deterministic equity-research platform covering US and Canadian companies, including mining producers. It normalises cost disclosures — C1 cash cost, total cash cost, AISC and AIC — from public SEC filings and licensed market data, and presents AISC margin and breakeven relative to prevailing metal prices alongside grade, jurisdiction and sustaining-capital context, so the same inputs always produce the same output. The material is educational: it organises the data investors examine as one input among many, and does not provide investment advice or recommendations.