The Greeks Explained: Delta, Gamma, Theta, Vega, Rho

Every options trader has to understand the Greeks. Here is exactly what each one measures, how they interact, and dollar-scale examples that make the numbers click.

The Greeks are the sensitivity measures that explain why an option's price changes. Delta measures direction. Gamma measures how delta itself changes. Theta measures time decay. Vega measures volatility exposure. Rho measures interest-rate sensitivity. Every profitable options trader can tell you, in seconds, what each of their positions is exposed to — and they use the Greeks to do it.

Delta: Directional Exposure

Delta is the change in option price for a $1 change in the underlying stock. It ranges from 0 to +1 for calls and 0 to -1 for puts.

• ATM call ≈ 0.50 delta — moves $0.50 for every $1 in the stock.
• Deep ITM call → 1.00 delta — behaves like 100 shares of stock.
• Deep OTM call → 0.00 delta — barely moves when stock moves.
• Put deltas are negative: ATM put ≈ -0.50.
• Delta also approximates probability of finishing ITM: a 0.30 delta call has roughly a 30% chance of expiring in-the-money.

Gamma: The Rate of Change of Delta

Gamma measures how much delta changes per $1 move in the stock. It is highest at-the-money and collapses for deep ITM or OTM options. Gamma is also highest near expiration — which is why 0DTE and weekly options behave so violently.

• Gamma is always positive for long options, always negative for short options.
• Short-dated ATM options have the highest gamma — a 1% move in the stock can flip the option from 40 delta to 60 delta overnight.
• High gamma = large P&L swings — good if you're right about direction, painful if wrong.
• Long options benefit from convexity — gains accelerate in your favor, losses decelerate.
• Short options suffer negative gamma — losses accelerate against you, which is why selling 0DTE without a stop is catastrophic in tail events.

Theta: Time Decay

Theta is the dollar amount your option loses per day simply from the passage of time. It is the price you pay for leverage and optionality.

• ATM 30-day option: theta might be -$0.05 per share per day = -$5 per contract per day.
• Theta accelerates as expiration approaches — last week can be -$0.20+ per day.
• Weekends count: Friday's theta decay includes Saturday and Sunday priced in.
• Long options = negative theta (paying time premium). Short options = positive theta (collecting).
• Theta is highest for ATM options because they have the most extrinsic value to decay.

Vega: Volatility Exposure

Vega is the dollar change in option price per 1 percentage-point change in implied volatility. Options expand and contract with IV — often independently of the stock moving.

• Long ATM 30-day option: vega ≈ $0.10 per 1% IV change per share = $10 per contract per 1% move.
• Vega is highest for ATM and longer-dated options; near-zero for deep ITM/OTM shorts.
• Long options = positive vega (benefit from IV expansion). Short options = negative vega (profit from IV crush).
• Pre-earnings IV rise — stock-specific vega can add 20-40% to option prices in the two weeks before earnings.
• Post-earnings IV crush — the day after earnings, IV often drops 30-50%. A +5% stock move with a -40% IV crush frequently leaves long calls unchanged or down.

Rho: Interest Rate Sensitivity

Rho measures option price change per 1 percentage-point change in the risk-free rate. For short-dated options it is usually negligible. For LEAPS (1-3 year options) and when rates are changing rapidly, rho becomes meaningful.

• Long calls = positive rho — higher rates slightly raise call prices (cost of carry).
• Long puts = negative rho — higher rates slightly lower put prices.
• Rho becomes a 5-10% factor in 2-year LEAPS when the Fed shifts 200+ bps.
• Most traders safely ignore rho for options under 90 days.

The Greeks Interact — You Are Never Exposed to Just One

Every option has all five Greeks simultaneously. A profitable trade requires the direction (delta), the velocity (gamma), the time frame (theta), and the volatility regime (vega) to align. Understanding the combination is what separates a trader from a gambler.

• Long weekly ATM call: high positive delta, high positive gamma, very negative theta, moderate positive vega. Needs a fast move in the right direction.
• Covered call: +100 delta from stock, -30 delta from sold call = +70 delta. Positive theta from the sold call collects daily. Negative vega (IV expansion hurts if forced to close).
• Iron condor: near-zero delta (market-neutral), negative gamma (hurts on big moves), positive theta (collects daily), negative vega (IV expansion hurts). Profit zone is a sideways market with IV contraction.
• Long LEAPS call: high positive delta (0.70+), low gamma, small theta, meaningful positive vega and rho. Behaves like stock with leverage.

Key Takeaways

• Delta = directional exposure. Gamma = how fast delta changes.
• Theta eats long options daily; high-gamma short-dated positions are theta-poisoned.
• Vega is why earnings plays lose even when direction is right — IV crush.
• All five Greeks are active on every option — never focus on delta alone.
• Positive-theta strategies (covered calls, credit spreads, iron condors) win from sideways markets; long-option strategies win from fast moves.