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Delta, gamma, theta, vega, rho — what each greek measures, what it tells you about a position, and how each one behaves differently on 0DTE.
The greeks are partial derivatives — measures of how an option's price changes when one of its inputs (underlying, time, volatility, interest rate) moves. Each greek isolates one sensitivity. Together they give you a working model of how a position will behave between now and expiration.
Start with Meet the Greeks for a one-paragraph intro to each, then walk the dedicated articles for the four that matter day-to-day: Delta, Gamma, Theta, and Vega. Rho gets a short article because for 0DTE it's essentially zero — included for completeness, not because you'll think about it.
The 0DTE angle changes how you weight each greek. Theta is large in absolute terms (the entire extrinsic value has to decay to zero within a single trading day) but realized theta isn't the smooth curve textbooks draw — it accelerates non-linearly toward the close. Gamma is the dangerous one: as expiration approaches, gamma concentrates at the strike, and a position that looked benign at 10am can have a substantially different risk profile by 3pm. Each article covers the 0DTE-specific behavior alongside the general theory.
The second-order greeks (charm, vanna, volga) get a single overview article — Charm, Vanna, Volga — with charm broken out into its own deeper dive in the dynamics module since it's central to 0DTE.
The greeks are how options react to changes in their inputs. One paragraph each on delta, gamma, theta, vega, and rho — plus how they combine in positions and why they matter most on 0DTE.
Delta has two interpretations — how much the option moves per $1 of underlying, and approximately the probability of finishing ITM. Both come from the same number. Plus how delta varies with strike, time, and IV, and what makes delta behave differently on 0DTE.
Gamma measures how delta changes as the underlying moves. Largest at ATM, especially near expiration. Why long-gamma and short-gamma positions behave so differently, and why 0DTE gamma is the structural reason short-premium trades blow through their expected ranges.
Theta is the rate at which an option loses value as time passes. Why it's largest at ATM, why it accelerates near expiration, what 'theta per day' means when there's less than a day left, and why every theta-collection trade is mechanically a bet against the gamma it pairs with.
Vega measures sensitivity to IV. Largest at ATM and for long-dated options; shrinks toward zero as expiration approaches. Why 0DTE vega is small in dollars but still meaningful in percent of premium, and what IV crush actually does to a position.
Rho is an option's sensitivity to the risk-free interest rate. For LEAPS and long-dated options it can matter. For 0DTE it's essentially zero. What rho measures, why it's small for short-dated options, and the rate environments where it's worth thinking about.
Beyond the main four greeks are second-order sensitivities — how the first-order greeks themselves change. Charm (delta with time), vanna (delta with IV / vega with spot), volga (vega with IV). What they are, when they matter, and why retail 0DTE traders can mostly ignore vanna and volga while charm is a real consideration.
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