For educational purposes only; not investment advice. Investing may result in loss.
Direct answer
The Cboe S&P 500 PutWrite Index (PUT) is a rules-based U.S.-dollar strategy benchmark, not a security or an account. It represents a hypothetical Treasury-bill portfolio overlaid with short, at-the-money SPX puts that are replaced monthly, usually on the third Friday. It does not hold S&P 500 stocks and cannot itself be bought directly; a fund, note, managed account, or options account referencing PUT is a separate product with its own documents and results.
Its economic return comes from Treasury interest plus put premium minus losses owed when SPX settles below the strike. Premium can cushion a flat or modestly declining market, but the strategy retains substantial equity downside. Repeated small premiums are not a guarantee against one severe decline.
This article describes the USD PUT benchmark under the Cboe S&P 500 PutWrite Indices Methodology version 3.0, last revised 2025-08-15, as checked on 2026-08-22. PUT has a base date of 1988-06-01 and launch date of 2007-06-20, so pre-launch values are back-tested. It does not determine suitability, margin, tax, disclosure, or legal treatment for any investor, account, product, or jurisdiction; those depend on current local rules and professional advice. “PutWrite index” is only a family description, and other variants can differ materially.
How the monthly rule works
The official PUT methodology combines 1- and 3-month U.S. Treasury bills with short, 1-month SPX puts held to maturity. On the monthly roll date, generally the third Friday or preceding business day for an exchange holiday, the expiring put settles in cash against the SPX Special Opening Quotation (SOQ). The new strike is the listed strike closest to but not above the last S&P 500 Index value reported before 11:00 a.m. ET; the new put is deemed sold at eligible-trade VWAP from 11:30 a.m. to 12:00 p.m. ET. Position size follows the published collateral formulas. On a simplified 1-period basis:
strategy ending value = collateral + collateral interest + put premium − max(K − S_T, 0) × put units
The premium is maximum option income, not maximum strategy profit: Treasury interest also contributes, and losses below the strike increase point for point. Cash collateral prevents borrowing from being the design’s return source, but it does not protect the collateral from being consumed by settlement losses.
Between rolls, the published level is Treasury-bill balances minus the marked short-put liability; the closing option mark uses the arithmetic average of the last bid and ask reported before 4:00 p.m. ET. A real account can differ because of commissions, spreads, taxes, execution timing, collateral yield, contract rounding, position limits, and inability to trade at methodology reference prices. The index is hypothetical and its pre-launch history is back-tested, not an investor’s realized return record.
A normalized one-month return
Consider an educational period normalized to collateral of 100. Sell an at-the-money put with strike 100 for premium 2.5, and assume collateral earns 0.3 during the month. Before fees and taxes:
| Index at settlement | Put settlement loss | Premium + interest | Strategy ending value | Period return |
|---|---|---|---|---|
112 |
0 |
2.8 |
102.8 |
+2.8% |
100 |
0 |
2.8 |
102.8 |
+2.8% |
98 |
2 |
2.8 |
100.8 |
+0.8% |
92 |
8 |
2.8 |
94.8 |
−5.2% |
80 |
20 |
2.8 |
82.8 |
−17.2% |
The one-period breakeven is 97.2: strike 100 minus premium and interest 2.8. The upside is capped at the premium plus collateral yield for that period, while downside below breakeven remains nearly point for point. At the next roll, the benchmark resets its strike and position using then-current levels; rolling does not recover the prior loss.
This table explains the payoff but does not reproduce every official index calculation detail. The methodology document, not this simplified example, governs published PUT values.
Interpretation checklist
- Distinguish the published benchmark from a fund, note, options account, or marketing backtest claiming to track it.
- Read the current methodology for version, underlying, strike rule, roll date,
SOQ, VWAP window, collateral instruments, and index adjustments. - Compare PUT with an appropriate total-return equity benchmark and cash rate over identical dates; do not compare a collateralized index with a price-only stock index.
- Separate option premium, Treasury yield, and settlement loss. Calling the entire return “volatility premium” overstates what the data prove.
- Examine drawdowns, worst months, recovery time, downside capture, beta, and tail outcomes rather than only annualized return or Sharpe ratio.
- Mark observations before
2007-06-20as back-tested and later observations as post-launch index history; neither establishes future execution. - Account for volatility regime and skew. Higher premium often accompanies higher expected or perceived downside risk.
- For replication, include spread costs, taxes, collateral yield differences, contract sizing, SPX cash settlement, and operational roll risk; verify account eligibility and local legal, tax, and disclosure rules separately.
Common misconceptions
- “PUT is an index of put prices.” It tracks a collateralized strategy portfolio, not a standalone option quote.
- “It owns the S&P 500 and sells puts.” The defined PUT portfolio uses Treasury bills plus short SPX puts.
- “Cash-secured means capital-protected.” Collateral funds losses when the index finishes below the strike.
- “Premium is free yield.” It is compensation received while assuming a contingent downside obligation.
- “A lower historical beta means no crash risk.” Nonlinear losses can be severe even when full-sample beta is below one.
- “The published index return is replicable without friction.” Rules-based reference prices, fees, taxes, liquidity, and collateral returns create tracking differences.
- “Every PutWrite index follows PUT.” Weekly, out-of-the-money, and other-underlying variants have different exposures.
Related topics
Authoritative sources
- Cboe S&P 500 PutWrite Indices Methodology - Governing constituents, selection, roll, pricing, collateral, calculation, dates, and methodology version.
- Cboe S&P 500 PutWrite Index Fact Sheet - Current index description, performance presentation, and back-test warning.
- Cboe Global Indices: PUT Index Dashboard - Current PUT identity and index dashboard.
- Cboe Index Roll Information - Dated PUT reference levels, strikes, VWAP prices, position sizes, and Treasury-bill rates.
- Characteristics and Risks of Standardized Options - Exchange-traded option characteristics, writer obligations, settlement, and risk disclosures.
- S&P 500 Index Options Product Specifications - SPX exercise style, cash settlement, contract multiplier, and trading specifications.