Mapping SPX GEX Levels to ES Futures Without Basis Errors
Translate cash-index gamma references onto futures charts using synchronized prices, contract-aware basis, and explicit uncertainty.
By OrderMap Research4 min read
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Two related instruments still have different prices
SPX is a cash index. ES is a futures contract linked to that index. They share economic exposure, but financing, expected dividends, remaining contract life, and market conditions create a difference between their price levels. Copying an SPX strike directly onto an ES chart can put a reference in the wrong place.
Here we define basis as futures price minus cash-index value. A simple local mapping adds that observed basis to the SPX reference. CME's explanation of equity index basis describes the relationship. Always confirm the sign convention, because some materials define the subtraction in the opposite direction.
Work through a synchronized example
Assume invented simultaneous observations: SPX at 6,000.00 and the selected ES contract at 6,026.50. Under our convention, basis is positive 26.50. An SPX gamma concentration at 6,020 maps locally to ES 6,046.50. A cash reference at 5,980 maps to ES 6,006.50.
| Reference | Hypothetical SPX level | Added basis | Mapped ES reference |
|---|---|---|---|
| Upper concentration | 6,020.00 | 26.50 | 6,046.50 |
| Current cash level | 6,000.00 | 26.50 | 6,026.50 |
| Lower concentration | 5,980.00 | 26.50 | 6,006.50 |
This is a price-coordinate conversion. It does not mean the SPX option strike has become an ES option strike, or that the underlying dealer position has changed. Nor does it establish the correct hedge ratio for a portfolio. Those are separate questions involving contract specifications and risk sensitivities.
If ES moves to 6,031.00 while SPX is still 6,000.00 in a genuinely synchronized observation, basis becomes 31.00 and the upper mapped reference becomes 6,051.00. A moving futures line can therefore reflect changing basis even when the original cash reference is unchanged.
