Understanding All-In Sustaining Cost and What It Leaves Out

All-in sustaining cost was introduced to give investors a fuller picture than cash cost. It succeeded in that narrow goal, but AISC remains a guidance metric rather than an accounting standard, and companies apply it differently enough that comparing two miners' AISC figures at face value is a common and avoidable analytical error.

Why cash cost was not enough

Cash cost measures only the direct expense of mining and processing ore, leaving out the capital a company must continually spend to keep a mine producing at the same rate. A company could report a low cash cost while its mine slowly degraded from underinvestment in sustaining capital, and investors comparing cash cost across companies had no way to see that trade-off. AISC was designed specifically to close that gap.

What it includes

Mining and processing costs, royalties, sustaining capital expenditure, and corporate general and administrative expense allocated to operations all sit inside AISC. That is considerably more honest than cash cost, which excludes the capital required to keep producing. By folding sustaining capital into the cost figure, AISC forces a company to show the true ongoing cost of running the asset as it exists today, not the cost of running it while deferring maintenance.

What it excludes

Growth capital, exploration beyond mine-site work, financing costs, taxes, and in most presentations, reclamation spending beyond the accrual all sit outside AISC. A company building a new mine can report attractive AISC on its existing operation while consuming cash overall once growth capital and financing costs are added back. This is the most common source of confusion: a headline AISC figure can look strong even while the company's overall free cash flow is negative, because the metric was never designed to capture the full capital program.

The by-product trap

Producers with meaningful by-product credits — silver or copper credits at a gold mine, for instance — often report costs net of those credits, which can produce very low or even negative AISC. That is arithmetic, not efficiency: it reflects the price of the by-product metal at the time of reporting as much as it reflects the underlying operation. It makes cross-company comparison meaningless unless you normalise for it, either by comparing gross costs before credits or by checking what commodity price assumptions were used to calculate the credit.

Why non-standardisation persists

Unlike revenue recognition or depreciation, AISC has no single governing accounting standard, even though an industry body has published guidance on its calculation. Companies retain discretion over what counts as "sustaining" versus "growth" capital, how corporate overhead is allocated between operations and head office, and how by-product credits are presented. That discretion is not necessarily evidence of manipulation, but it means the metric is best used to track a single company's own cost trend over time, where the methodology is at least internally consistent, rather than as a precise ranking tool across an entire sector.

Comparing across jurisdictions

Costs allocated to sustaining capital, royalties and reclamation accruals can also vary by jurisdiction, since royalty regimes and reclamation obligations differ by country and even by province. Two operations with identical mining costs can report different AISC purely because of where they are located, which is a further reason to treat AISC as most reliable for tracking a single asset over time rather than for ranking companies operating in different jurisdictions against one another, particularly when comparing operations across borders.

How to use AISC well

The most reliable approach is to read the reconciliation table in the notes to the financial statements, where a company breaks AISC down into its components, rather than relying on the single headline number in a press release. Watching the trend in sustaining capital as a share of total AISC over several quarters can reveal whether a company is deferring maintenance to protect the headline figure, which would show up later as a cost spike or an unplanned production shortfall.

What to watch

Track the AISC reconciliation disclosed in quarterly filings, the split between sustaining and growth capital, changes in by-product credit assumptions relative to prevailing metal prices, and whether guidance revisions to AISC coincide with revisions to sustaining capital estimates rather than operating cost improvements.