Free Online Cutoff Grade Calculator: Breakeven Gold and Base Metals

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Cutoff grade is cost divided by recovered value per grade unit. The breakeven cutoff pays every cost including mining and defines what enters the mine plan; the internal cutoff drops the mining cost, because rock already on the truck only has to out-earn the mill: process it or dump it.

Where rock becomes ore

Ore is an economic word, not a geological one: rock is ore only when a tonne of it pays its own way. The tool above computes that boundary. Recovered value per grade unit comes from metal price, plant recovery, and smelter payability; dividing costs by it gives the cutoff. Precious metal mode works in grams per tonne against a price per troy ounce; base metal mode works in percent against a price per tonne of metal. You get both cutoffs that matter: breakeven, which includes mining cost, and internal, which does not.

Chart of revenue per tonne rising with grade against a flat cost per tonne line, with the crossing point marked as the cutoff grade
The grade at which one tonne pays exactly its own costs, given price, recovery, and payability.

Within the Mining and Resource Suite this is the economic knife: the grade-tonnage curve shows what the deposit offers, and the cutoff decides where to slice it.

The distinctions that pay

  • Breakeven cutoff defines the mine plan: rock below it should never be scheduled for processing in the first place.
  • Internal cutoff governs rock already being moved: on the truck, mining cost is spent either way, so mill it if it beats processing plus overhead alone.
  • Recovery and payability quietly halve or rescue projects: 90 percent recovery at 95 percent payability strips 15 percent off gross value before any cost is paid.
  • Cutoffs move with prices: a long-life mine recalculates them constantly, which is why marginal stockpiles exist.

What this tool is for

Screening drill results against real economics, setting reporting cutoffs for resource statements, and teaching the breakeven versus internal distinction. Full cutoff optimization adds opportunity cost and mill capacity constraints in the tradition of Lane; these two numbers are its foundation.

Related Calculators and Reference

Common Questions

How is cutoff grade calculated?

Divide the cost per tonne by the recovered value per grade unit, which comes from metal price, plant recovery, and smelter payability. The result is the grade at which one tonne exactly pays its way.

What is the difference between breakeven and internal cutoff?

Breakeven cutoff includes mining cost and decides what enters the mine plan. Internal cutoff drops the mining cost, because rock already on the truck only needs to out earn processing: mill it or dump it.

Does cutoff grade change with metal price?

Yes, continuously. Higher prices lower the cutoff and turn waste into ore, which is why long life mines recalculate cutoffs and keep marginal stockpiles.