25-delta put IV - 25-delta call IV = 3-5 vol points (SPX)
| source | CBOE option chain history |
| derivation | data_calibrated |
| quality | calibrated |
| set | 2026-05-25 |
| last reviewed | 2026-05-25 |
| next review due | 2026-12-31 |
Persistent skew vs symmetric Black-Scholes assumption; used in M-131 + M-136 vol surfaces.