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Index Options vs. Stock Options

An index option is an option on a stock index -- a basket such as the S&P 500 or Israel's TA-35. A stock option is an option on the shares of one company. Both give the buyer a right for a premium, and their payoff at expiration is calculated the same way. What differs is what you are exposed to, how the contract settles, when it can be exercised and how large it is. This guide from OptionLab (option-graph.com) compares the two side by side and works through one example of each.

The Differences at a Glance

FeatureStandard US stock optionS&P 500 index option (SPX)TA-35 index option (Israel)
UnderlyingShares of one companyThe S&P 500 indexThe TA-35 index
Exercise styleAmericanEuropeanEuropean
SettlementDelivery of 100 sharesCashCash; in-the-money options exercised automatically
Contract size100 sharesIndex × $100Index × NIS 50

The sources are the exchanges and regulators themselves: FINRA's investor guidance says equity options trade American-style and index options generally trade European-style and settle in cash; Cboe's SPX specification gives the $100 multiplier and European exercise; and the Tel Aviv Stock Exchange (TASE) specifies the TA-35 contract at NIS 50 per index point. Exceptions exist, so check the specification of the exact contract. The payoff calculators on option-graph.com let you set the contract size, so the same tool works for both kinds.

Settlement: Cash vs. Shares

Exercising a stock call means buying 100 shares at the strike; exercising a stock put means selling them. The result is a stock position you then hold or sell. An index cannot be delivered, so index options settle in cash: the holder receives the difference between the settlement value and the strike, times the multiplier. For SPX, Cboe computes the settlement value from the opening prices of the index's stocks on the expiration date; TASE uses opening prices of the constituents for the TA-35 expiry index. Either way, the settlement value is not the last index level you saw the evening before. On option-graph.com both kinds of results are shown simply as money per contract.

Two Worked Examples

Index call. Suppose an index is at 5,000 (an illustrative level, not market data) and you buy a call with a 5,000 strike for 80 index points. With a $100 multiplier, that costs $8,000. If the settlement value at expiration is 5,150, the call pays 150 points, or $15,000, and the result is +$7,000. No shares change hands; the difference is paid in cash. The chart below uses the same expiration formula as the calculators on option-graph.com.

Stock call. You buy a call on a $100 stock with a $100 strike for $3.00 per share, or $300 per contract. If the stock is at $106 at expiration and the call is exercised, you buy 100 shares at $100 that are worth $106. Net of the premium, the result is +$300 -- but you now hold $10,600 of stock, with its own risk, unless you sell it or close the option before expiration. Both positions can be entered on option-graph.com to compare their payoff lines.

Index call at expiration: 5,000 strike, 80-point premium

↕ Profit / loss per contract ($)↔ Settlement value at expiration (index points)
Index call at expiration: 5,000 strike, 80-point premiumA payoff line flat at a loss of 8,000 dollars up to the 5,000 strike, then rising 100 dollars per index point, crossing zero at 5,080 and reaching a profit of 22,000 dollars at 5,300.-10,000010,00020,0004,8004,9005,0005,1005,2005,300K 5,000BE 5,080

Profit zoneLoss zoneK = StrikeBE = Breakeven

Key values
PointUS dollars per contract (index × $100)
Strike 5,000−8,000
Breakeven 5,0800
P/L at 4,800−8,000
P/L at 5,300+22,000
Profit or loss of one index call with a $100 multiplier, by settlement value from 4,800 to 5,300. The loss is capped at the $8,000 premium; the breakeven is 5,080. The index level is illustrative.Units: US dollars per contract (index × $100)Assumptions:
  • Multiplier $100 per index point
  • Premium 80 points, $8,000 per contract
  • Cash-settled at expiration; commissions excluded

What Moves the Price

A single stock can jump on one company's earnings, a takeover or a lawsuit. An index spreads that risk over many companies, so its moves are usually smaller -- though a market-wide shock hits every stock in it at once. That difference shows up in implied volatility, and implied volatility drives the premium. For an at-the-money call with 30 days left, the Black-Scholes value is about 1.9% of the underlying price at 15% volatility and about 4.2% at 35%. The volatility levels here are illustrative, not quotes for any index or stock; the curve below shows the whole range, computed the way option-graph.com computes theoretical values. The Black-Scholes calculator on option-graph.com lets you change volatility and watch the premium respond.

Premium of an at-the-money call by implied volatility

↕ Call value per contract ($)↔ Implied volatility
Premium of an at-the-money call by implied volatilityA rising, almost straight line: about 131 dollars at 10% implied volatility, about 188 dollars at 15%, about 302 dollars at 25%, about 416 dollars at 35% and about 587 dollars at 50%.020040060010%20%30%40%50%

Value before expiry (Black–Scholes)

Key values
PointValue before expiry (Black–Scholes)
10%131.34
25%302.11
50%587
Black-Scholes value of one at-the-money call on a $100 underlying with 30 days left, as implied volatility changes from 10% to 50%. Higher volatility, typical of single stocks, means a higher premium.Units: US dollars per contract (100 units)Assumptions:
  • Underlying $100, strike $100, 30 days left, rate 4%, no dividends
  • Only implied volatility changes
  • Black-Scholes model: theoretical values, not market quotes

When Each One Fits

  • Hedging a diversified portfolio: index options follow the market as a whole; one contract can cover broad market risk, though not the exact portfolio.
  • A view on one company: stock options follow that company, including events that an index would dilute.
  • Avoiding a stock position: cash-settled index options never leave you holding shares after expiration.
  • Early assignment: writers of American stock options can be assigned before expiration; with European index options, assignment follows expiration only.

Whichever you choose, size matters: one index contract can represent a much larger amount of money than one stock contract. Before trading, compare the notional value -- index level times multiplier -- with your account, and test the position on option-graph.com.

Risks and Limitations

Index options are cash-settled, but writers can still lose far more than the premium received. Stock options add the risk of early assignment and of ending up with a stock position you did not intend. Contract terms differ between exchanges and products, and they can change. The prices and volatility levels in this article are illustrative, so rerun the numbers with current quotes on option-graph.com before you trade. Options are not suitable for every investor. OptionLab (option-graph.com) is an educational and analytical tool and does not provide investment advice.

Summary

  • Index options cover a basket and usually settle in cash; standard stock options cover 100 shares and settle by delivery.
  • Index options are generally European; US stock options are American.
  • Contract size differs widely: SPX is index × $100, TA-35 is index × NIS 50.
  • Single stocks usually carry higher implied volatility, so their options cost more relative to price.
  • Read the contract specification, then compare both on option-graph.com before deciding.
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