InsightsPricingSeptember 2026 · 7 min read

Theta and gamma: the trade you're always making

Every option position is a bet on whether the stock will move more or less than implied volatility says. Black–Scholes tells you exactly where the break-even is.

By Shrey Desai

The Black–Scholes equation on our home page looks academic. Inside it is the single most practical idea in options trading: time decay and the benefit of movement are two sides of one coin.

What the equation balances

For a delta-hedged option, ignoring interest rates, the equation reduces to a simple balance:

Θ + ½ σ² S² Γ ≈ 0

Theta (Θ), the value an option loses each day, is paid for by gamma (Γ), the profit from the stock moving, when the stock moves exactly as much as implied volatility (σ) predicts.

If you own an option, you pay theta every day. In return you earn gamma whenever the stock moves. If the stock moves more than implied volatility says, gamma wins. If it moves less, theta wins. If you sell the option, the same trade runs the other way.

The daily break-even move

You can turn implied volatility into the daily move the market expects. Divide annual volatility by the square root of the number of trading days in a year (about 252, whose square root is about 15.9):

Worked example

Stock at $100, implied volatility 32%.

Daily move ≈ 100 × 0.32 ÷ 15.9 ≈ $2.02, about 2% a day

A long option holder needs the stock to move about 2% a day, on average, to break even on time decay. Days of 0.5% moves bleed money even if the stock drifts the right way. A few 4% days can pay for weeks of decay.

Why this changes how you choose trades

  • Buying options is a bet that realised volatility will beat implied volatility. It is not simply a bet on direction.
  • Short-dated options have the most gamma and the fastest theta. They're cheap in dollars but expensive in daily decay.
  • Events concentrate movement. Earnings, product launches and macro releases are where realised volatility is most likely to beat what's priced, if the implied move is reasonable. See reading the implied move.

To see this in action, open the Strategy Lab, choose Long call, and drag Days elapsed forward. The dashed line sinks toward the expiry payoff. That sinking is theta, and the curvature of the line is gamma.

Educational content only, not investment advice. Figures are hypothetical. See our disclosures.