Delta

Delta is how much an option's price changes per $1 move in the stock — a volume knob on direction. Call deltas run 0 to +1, put deltas 0 to −1, and one contract's delta × 100 is its share-equivalent exposure: a 0.62-delta call trades like 62 shares.

Delta's second job is the odds shortcut: it approximates the probability the option finishes in the money. A 0.30-delta call carries roughly 30% finish-ITM odds. The shortcut is a model estimate quoted in current implied volatility — the gap versus true odds widens with time and vol, and it never tells you how big a win or loss is, only how often.

Premium sellers use the delta dial to pick strikes: selling the ~0.30-delta cash-secured put means roughly 30% assignment odds and ~70% odds of keeping the premium, while the 0.15-delta strike halves the odds and the paycheck. Deltas also add across a book — 100 shares plus a short 0.30-delta call nets to +70 share-equivalents.

The interactive explorer draws the full delta-vs-stock-price S-curve for calls and puts, with a spot slider, days-to-expiry buttons, and live stats for delta, ≈P(finish ITM), and share-equivalent exposure. Delta is a snapshot, not a contract — how fast it goes stale is gamma's story.