Same index, in three currencies.

Three instruments, one index

SPX is the cash index itself — a calculation, not something you can hold. SPY is an ETF that owns the underlying basket, and ES is a futures contract priced off the index. All three track the same thing, which is why traders quote levels interchangeably, and none of them are the same instrument.

The conversions are ratios rather than identities. SPY trades near SPX ÷ 10 and ES trades near SPX itself, but "near" is doing real work in both cases. Keeping the ratio editable matters because the correct value drifts over the year rather than sitting at a constant.

A worked example

With SPX at 5,000 and the ratio at 10.0, SPY prints around $500. One ES contract at 5,000 carries 5,000 × $50 = $250,000 of notional — roughly the size of a house, controlled with a few thousand dollars of day margin.

The same exposure in SPY would be 500 shares at $500, or $250,000 of stock. That equivalence is the practical use of the converter: sizing a hedge in one instrument against a position held in another, without accidentally being off by a factor of ten.

Where this calculator misleads you

The three instruments do not trade in lockstep at the edges. ES runs nearly 24 hours while SPY is bound to the equity session, so overnight moves show up in ES first and gap into SPY at the open. A conversion computed at 3am describes where SPY should open, not where it last traded.

The SPY-to-SPX ratio is not a constant. Dividends paid out of the ETF and its expense ratio pull it below a clean 10 over time, then quarterly rebalancing nudges it back. Using a stale ratio introduces a small error that scales directly with position size.

Nothing here is a live quote. The tool computes relationships between prices you supply, which keeps it free and shareable but means the output is only as current as the numbers you type.

Terms on this page

SPX

The S&P 500 cash index. A calculated value — options settle on it, but it cannot itself be bought or sold.

ES

E-mini S&P 500 future, $50 per index point. Nearly 24-hour trading, quarterly expiry.

MES

Micro E-mini, one tenth of ES at $5 per point. The retail-sized version of the same exposure.

Fair value

The expected gap between a future and the cash index, driven by interest to expiry minus expected dividends.

Expense ratio

Annual fee taken from ETF assets. One of the two forces pulling SPY below a clean SPX ÷ 10.