Theta Harvesting

Theta harvesting is the practice of selling options to collect their time decay. Because options lose extrinsic value as expiration approaches, sellers profit if the underlying does not move enough to offset that decay. The strategy works on average because implied volatility has tended to be higher than the volatility that actually occurs, a gap known as the volatility risk premium. The catch is that sellers occasionally suffer large losses when markets move sharply.

The volatility risk premium#

Investors pay up for options, especially index puts, because they want protection. As a result, implied volatility on the S&P 500 has historically averaged a few points above the realised volatility that followed. Sellers of options collect that difference over time, like an insurer collecting premiums. See Implied Volatility (IV) and Historical and Realized Volatility.

Cboe publishes indices that track systematic option selling, such as the BuyWrite (BXM) and PutWrite (PUT) indices on the S&P 500. Over long periods, these have produced returns comparable to the index with lower volatility, but with sharp drawdowns in crashes such as 2008 and 2020.

Common theta harvesting structures#

Typical rules#

Many option sellers follow rules like these, which are widely discussed rather than proven optimal:

• Open at 30 to 45 days to expiry, where decay is meaningful but gamma is still moderate.
• Sell around 15 to 30 delta strikes.
• Take profits at 50% of the maximum premium rather than holding to expiry.
• Close or roll at about 21 days to avoid the high gamma of the final weeks.
• Size small so that a full loss on any position is tolerable.

The tail risk problem#

Option selling has negative skew: many small wins and occasional large losses. Famous blow ups include:

• February 2018: a sudden spike in the VIX led to the collapse of several short volatility products, including an exchange traded note that lost most of its value in a day. See The VIX.
• 2018: an options management firm, OptionSellers.com, lost large sums of client money on short natural gas call options when prices spiked in November.
• March 2020: the COVID crash caused severe losses for many put sellers. See The COVID-19 Crash.

Surviving as a premium seller#

1. Use defined risk structures (spreads, condors) rather than naked options.
2. Size by worst case, not by expected profit. See Position Sizing.
3. Diversify across underlyings, expiries and directions, while remembering that correlations jump in crashes. See Correlation Management.
4. Reduce exposure when implied volatility is very low, since premiums are small and risks are not. See IV Rank and IV Percentile.
5. Have a plan for big moves: where to close, roll or hedge.
6. Track short gamma and vega across the whole book. See Managing Portfolio Greeks.

Common mistakes#

• Mistaking a high win rate for a safe strategy.
• Oversizing after a long winning streak. See Overconfidence.
• Selling naked options on volatile stocks for high premiums.
• Holding through expiry week for the last few cents.

Frequently asked questions#

What is theta harvesting?#

Selling options to collect time decay and the volatility risk premium, profiting if the underlying does not move too much before expiry.

Is selling options profitable?#

On average, option sellers have tended to earn the volatility risk premium, but losses in crashes can be large, so sizing and defined risk are essential.

What is the volatility risk premium?#

The tendency for implied volatility to exceed the volatility that later occurs, which rewards option sellers for bearing crash risk.

Next, learn how traders take views on volatility itself in Vega Positioning.

Sources#

• Cboe, Benchmark indices