Key takeaways
  • SPXW puts with 0–5 days left won on risk-adjusted returns
  • Far out-of-the-money strikes did best
  • Hybrid sizing balanced return and drawdown control
  • Kelly and VIX were tested as sizing rules

If you are selling S&P 500 puts, the smallest time windows may be the smartest bet. This paper studies systematic put-writing on SPXW options with expirations from 0 to 5 days, where the market’s implied volatility often exceeds realized volatility. It compares three ways to size positions: the Kelly criterion, VIX-based volatility regime scaling, and a hybrid that combines both. Across the design space, ultra-short-dated, far out-of-the-money options delivered superior risk-adjusted returns. The hybrid sizing approach stood out for balancing return generation with drawdown control, especially in low-volatility conditions such as those seen in 2024. The message is practical: harvesting the volatility risk premium is not just about picking the right option, but also about scaling exposure in a way that adapts when market conditions change.

A put sale can look safe right up until the market jolts. This study says the real edge sits in a small window. The best results came from SPXW options with 0 to 5 days left. These are S&P 500 index options with almost no time left. The strongest risk-adjusted returns came from ultra-short-dated, far out-of-the-money options, meaning strike prices far from the current index level. That is not the trade many people expect to win. Most would guess a longer bet gives more room to breathe. Here, the opposite looked better. When you sell volatility, meaning you bet that swings stay small, size matters as much as strike.

Why 0 to 5 days beat longer bets

The paper compared three sizing rules. Kelly sizing, a rule that aims for long-run growth, sets exposure from the edge. VIX-based scaling uses the volatility index, a market gauge of expected swing, to change exposure. The hybrid rule blends both signals. Across the design space, the same pattern kept showing up. Ultra-short-dated, far out-of-the-money contracts gave the best risk-adjusted returns. Risk-adjusted returns mean gains after risk is counted. The hybrid rule also helped control drawdowns, meaning drops from a high point. That mattered most in low-volatility conditions, including 2024. The calm regime did not erase the edge. It changed how much risk the strategy could carry. The hybrid kept the trade usable when the market mood softened.

How the sizing rules were tested

The test space was broad. It changed the moneyness level, which means how far the strike sits from the market price. It changed the volatility estimator, which is the rule used to guess future shake. It changed the memory horizon, which is how far back the model looks for clues. The study also used short expiry windows from 0 to 5 days. SPXW options with 0 to 5 days to expiry anchored the test. That let the same idea face many market moods. The point was not to find one perfect setting. The point was to see which sizing rule kept working as conditions changed. That design makes the result harder to dismiss as a one-off trade. It tests the strategy as a system, not a lucky day.

0–5days

expiry window tested on SPXW options

longer-dated contracts
  • Kelly criterion sizes the bet for long-run growth.
  • VIX-based scaling changes size when the volatility mood changes.
  • The hybrid rule mixes both signals to balance return and drawdown.

“The hybrid sizing method consistently balances return generation with robust drawdown control, particularly under low-volatility conditions such as those seen in 2024.”

From the abstract

Why the hybrid rule changes the game

For a portfolio desk, this shifts the main question. It is not just which strike to sell. It is how much size to carry in the current regime. A regime is a market mood, such as calm or tense. The hybrid rule tries to keep that size flexible. That matters because the volatility risk premium is the gap between implied and realized volatility. Implied volatility is the market's forecast of swing. Realized volatility is the swing that later shows up. The strategy tries to harvest that gap without letting one bad spell do too much damage. That makes short-dated put writing feel less like a fixed bet and more like a dial.

The stress test that still matters

The surprise is that tiny time windows can carry the strongest risk-adjusted edge. That makes size control the main lever. A desk can now treat SPXW put selling as a live dial, not a fixed bet. The hybrid rule gives that desk a way to adapt when calm markets make risk look small. Calm markets can hide trouble until it arrives fast. The next hard check is a sharp VIX spike. That is where the hybrid must cut risk without killing the edge. If it can do that, short-dated put writing becomes easier to run with discipline.