Options Greeks Explained: Delta, Gamma, Theta, Vega

The Greeks are the essential risk metrics for options trading. They tell you how sensitive your option’s price is to changes in the underlying stock price, time, and volatility. Understanding them is the difference between gambling and informed trading.

Delta — Directional Exposure

Delta measures how much an option’s price changes when the underlying stock moves $1.

Key facts:

• Call options have Delta between 0 and 1.0
• Put options have Delta between -1.0 and 0
• At-the-money options have Delta near 0.50 (calls) or -0.50 (puts)
• Deep in-the-money options approach 1.0 (or -1.0 for puts)

Practical use: If you own a call with 0.60 Delta, your option gains approximately $0.60 for every $1 the stock rises. It also means you have roughly a 60% probability of the option expiring in-the-money.

Portfolio Delta: Sum up the Deltas of all your positions to understand your overall directional exposure. A portfolio Delta of +100 means you’re effectively long 100 shares.

Gamma — Rate of Change

Gamma measures how fast Delta changes when the stock price moves $1. It’s the acceleration of your position.

Key facts:

• Gamma is highest for at-the-money options near expiration
• Long options have positive Gamma (Delta moves in your favor)
• Short options have negative Gamma (Delta moves against you)
• Gamma increases dramatically as expiration approaches

Practical use: High Gamma means your Delta is unstable. A short option position with high Gamma can quickly shift from market-neutral to heavily directional if the stock makes a sudden move.

Why it matters for sellers: Negative Gamma is the primary risk for premium sellers. A stock that gaps through your short strike can cause rapid, accelerating losses.

Theta — Time Decay

Theta measures how much value your option loses each day, all else being equal. Time is constantly working against option buyers and in favor of option sellers.

Key facts:

• All options have negative Theta (they lose value over time)
• Theta accelerates as expiration approaches
• At-the-money options have the highest Theta
• Theta is expressed as a daily dollar amount

Practical use: If your option has Theta of -0.05, it loses $5 per contract per day just from the passage of time. Over a week, that’s $35 in time decay.

For sellers: Positive Theta is how credit spread and iron condor strategies generate income. You collect premium upfront and profit as time erodes the option’s value.

Vega — Volatility Sensitivity

Vega measures how much an option’s price changes when implied volatility moves 1 percentage point.

Key facts:

• All options have positive Vega (higher IV = higher option prices)
• Longer-dated options have higher Vega
• At-the-money options have the highest Vega
• Vega decreases as expiration approaches

Practical use: If your option has Vega of 0.10 and implied volatility rises from 30% to 35%, your option gains approximately $0.50 per contract (0.10 x 5 points).

For income strategies: Iron condors and credit spreads have negative Vega exposure. An IV spike (like before earnings) can cause unrealized losses even if the stock hasn’t moved.

How the Greeks Work Together

The Greeks don’t act in isolation. Here’s how they interact:

Example: Long Call Option

Greek	Value	Meaning
Delta	+0.50	Gain $0.50 per $1 stock rise
Gamma	+0.05	Delta increases by 0.05 per $1 move
Theta	-0.03	Lose $3/day from time decay
Vega	+0.08	Gain $0.08 per 1% IV increase

If the stock rises $2 tomorrow, your position gains approximately:

• From Delta: $0.50 x 2 = $1.00
• From Gamma: $0.05 x 2 / 2 = $0.05 (additional gain)
• From Theta: -$0.03 (time decay cost)
• Net gain: ~$1.02 (assuming constant IV)

Using Greeks in Beefi.ai

Our options backtesting engine calculates all four Greeks at every point using the Black-Scholes pricing model. When you backtest a strategy, you can see:

• How Delta evolved throughout the trade
• When Gamma risk spiked near expiration
• How much Theta you collected daily
• The impact of volatility changes on your P&L

This level of detail helps you understand not just whether a strategy was profitable, but why it was profitable (or wasn’t), so you can make better decisions going forward.