Acceleration/Deceleration Oscillator
The Acceleration/Deceleration Oscillator (AC), developed by Bill Williams, measures whether the momentum of price movement (captured by the Awesome Oscillator) is accelerating or decelerating, functioning as a leading derivative of the AO signal.
Bill Williams positioned the Acceleration/Deceleration Oscillator as a refinement of the Awesome Oscillator — one step closer to the leading edge of price movement. The AO measures the difference between short- and long-term momentum; the AC measures the rate of change of that difference — effectively, the second derivative of price. Williams believed that the AC would change direction before the AO, and the AO would change direction before price itself, providing progressively earlier signals at each level of the hierarchy.
The AC is calculated by subtracting a 5-period SMA of the AO from the AO itself. The resulting histogram shares the same green-when-rising, red-when-falling colour convention as the AO. When the AC is above zero, the momentum (AO) is accelerating upward; when below zero, momentum is decelerating or negative.
For trading signals, Williams specified different rules depending on whether the AC is above or below the zero line. To enter a long position, the AC must produce two consecutive green bars if it is above zero (confirming acceleration in the positive zone), or three consecutive green bars if it is below zero (requiring more confirmation before assuming momentum has shifted from a negative zone). The inverse applies for short entries. This asymmetric confirmation requirement reflects the intuition that trading with the momentum zone (above zero for longs) requires less confirmation than trading against it.
The AC's sensitivity to rapid changes in the AO makes it prone to false signals in markets with irregular volatility. On intraday NSE charts — particularly 15-minute or hourly charts of Bank Nifty during high-volatility events such as RBI policy announcements or results season — the AC generates frequent histogram fluctuations that can produce whipsaw signals without Alligator or Fractal context. Practitioners using the full Williams system treat the AC as one of five confirming indicators rather than a standalone entry signal.
The AC is available as a standard indicator on TradingView (label: 'AC'), Kite by Zerodha, and Amibroker's built-in library.