What is an option's delta, in plain words?
Delta estimates how much an option's price changes for a $1 move in the stock 1. A call near the stock's price has a delta of about 0.50; deep in the money it moves toward 1.00, and far out of the money toward 0 1. It changes all the time, as the stock moves and as expiry nears 1.
A call with a $50 strike at 30% implied volatility (made-up numbers). Move the stock and the days left, and read the delta the formula gives.
From delta to dollars
With the stock at $50 and 30 days left, the call above has a delta of 0.53 by the formula 2: a $1 rise adds about 53 cents a share, or $53 for a contract of 100 shares, for a small move. For bigger moves delta itself changes 1, so the estimate drifts.
Why it bends near expiry
Close to expiry an option is worth little more than its intrinsic value, which is zero below the strike and rises dollar for dollar above it 3. So, with a few days left, delta moves quickly from near 0 to near 1 across a few dollars around the strike: move the days down to see the curve steepen.
What this shows, and what it doesn't
The formula's delta for one strike and one volatility. By the same formula a put's delta is negative: it gains as the stock falls 2. Delta is an estimate for small moves, not a promise for large ones.
Go further
Sources (3), checked 20 October 2026 and 27 October 2026
- The Options Industry Council, “Delta”. Read it (read 20 October 2026)
- Fischer Black and Myron Scholes, “The Pricing of Options and Corporate Liabilities”, Journal of Political Economy 81(3), 637–654, 1973. Read it (read 20 October 2026)
- The Options Industry Council, “What is an Option?”. Read it (read 27 October 2026)
Now try it on a scenario of your own
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