PutWrite Index: Premium Income with Collateralized Equity Downside
For educational purposes only; not investment advice.
Direct answer
Section titled “Direct answer”The Cboe S&P 500 PutWrite Index (PUT) is a rules-based strategy benchmark. It holds a Treasury-bill account and overlays short, at-the-money SPX puts that are replaced monthly, usually on the third Friday. It measures a collateralized put-writing process; it does not hold the S&P 500 stocks and is not itself a security that can be bought directly.
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.
“PutWrite index” is a family description, not one universal methodology. Other benchmarks may use different underlyings, moneyness, frequencies, collateral, roll prices, or settlement conventions. Research must name the exact ticker and methodology version.
How the monthly rule works
Section titled “How the monthly rule works”The official PUT methodology combines one- and three-month Treasury bills with short, one-month, at-the-money SPX puts. The number of puts is determined under the index rules so the portfolio value is not negative at rebalancing. On a simplified one-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.
The benchmark applies specified selection, pricing, roll, and valuation rules. A real account can differ because of commissions, bid-ask spreads, taxes, execution timing, collateral yield, position limits, and inability to trade at the methodology’s reference price. Index history may also include back-tested periods; it is not an investor’s realized return record.
A normalized one-month return
Section titled “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
Section titled “Interpretation checklist”- Distinguish the published benchmark from a fund, note, options account, or marketing backtest claiming to track it.
- Read the current methodology for underlying, strike rule, roll date, reference price, 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 which observations are live and which are back-tested. Historical and hypothetical performance do not establish 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.
Common misconceptions
Section titled “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
Section titled “Related topics”Authoritative sources
Section titled “Authoritative sources”- Cboe S&P 500 PutWrite Indices Methodology - Cboe Global Indices
- Cboe S&P 500 PutWrite Index Fact Sheet - Cboe Global Indices
- Characteristics and Risks of Standardized Options - Options Clearing Corporation
- Options - FINRA