Index-based pricing
Index-based pricing ties a contract price to a published market index, such as LME aluminum, COMEX copper, or a resin price index, through an agreed formula. The price adjusts on a set cadence as the index moves, often with a time lag, an adjustment threshold, and caps or collars. It protects both parties from volatility: neither side wins or loses on commodity swings nobody controls.
Examples
Copper-indexed cable assembly: An assembly contains 1.8 kg of copper. The contract sets a $14.60 base price at a $9,000-per-ton baseline, adjusting quarterly with a one-quarter lag when the average moves more than 4 percent. Copper averages $9,720, up 8 percent, so the next quarter's price becomes $14.60 plus 1.8 kg times $0.72 per kg, about $15.90.
Collared resin: A molder and buyer index polypropylene parts to a resin index with a collar of plus or minus 10 percent per year. When the index jumps 22 percent in 2025, the buyer's price rises only 10 percent, and the parties revisit the base at renewal as the contract specifies.
Audit catch: A quarterly adjustment uses the month-end index value instead of the contracted three-month average, overstating the increase by $0.11 per unit across 250,000 units. The $27,500 error is credited after the buyer's formula check.
Definition
Fixed prices on commodity-heavy parts force someone to bet on the market. If copper spikes, the supplier eats it or quietly degrades service; if it falls, the buyer overpays. Indexing removes the bet. A typical construction: unit price equals a base price plus the difference between the current index average and a baseline, multiplied by the commodity content per unit. The negotiable mechanics sit around that formula: which published index, what averaging period, what lag (one quarter is common), what threshold triggers an adjustment (plus or minus 3 to 5 percent is typical), and whether a collar caps movement in either direction.
Indexing is the formula-driven cousin of a general price escalation clause, and it differs from dynamic pricing, where sellers reprice continuously at their own discretion. The buyer's homework is the content figure. Indexing 100 percent of a part's price to copper when copper is 40 percent of its cost hands the supplier a windfall on every rally. That content estimate comes from cost modeling, the kind of work described in AI-assisted direct material cost modeling.
Indexed contracts also need auditing. Someone must verify each adjustment against the published index, or price variance creeps in through misapplied formulas and conveniently chosen dates. Platforms like LightSource tie quoted and contracted prices to the underlying indices, which makes that audit a query instead of a spreadsheet project.
Related Terms
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