OscillatorsLeading momentum-acceleration oscillatorAC

Accelerator Oscillator AC

Measures the acceleration of momentum — whether the driving force behind price is speeding up or slowing down.

Quick answer: The Accelerator Oscillator measures the acceleration or deceleration of momentum by subtracting a 5-period average of the Awesome Oscillator from the Awesome Oscillator itself, warning of momentum changes before they reach price.

In simple words

The Accelerator Oscillator takes momentum one step further than the Awesome Oscillator. Where the AO measures the force behind price, the AC measures whether that force is speeding up or slowing down — its acceleration. It subtracts a 5-period average of the AO from the AO, plotting the result as a green-and-red histogram around zero. Bill Williams argued that acceleration changes before momentum, and momentum changes before price — so the AC is meant to give the earliest warning of a coming turn. Green bars mean the force is accelerating, red bars decelerating.

Accelerator Oscillator — visual

How Accelerator Oscillator looks on a chart

The Accelerator Oscillator is the Awesome Oscillator minus its 5-period average, plotted as a histogram around zero. Green bars show accelerating momentum, red decelerating; it aims to signal changes before the AO or price.

Professional explanation

Acceleration, the derivative of momentum

If the Awesome Oscillator measures momentum, the Accelerator measures its rate of change — acceleration. The AC = AO − SMA₅(AO). When the AO is rising faster than its own recent average, the AC is positive and green; when the AO is slowing, the AC turns down and red even while the AO is still rising. This makes the AC a second-derivative-style tool: it flags the moment the driving force begins to change, which Bill Williams believed precedes the change in momentum and, in turn, in price.

Bar colour is the primary signal

For the AC, colour matters more than the zero line. A green bar means momentum is accelerating; a red bar means it is decelerating. Bill Williams' rule is notably strict: you should not buy with a red bar, and you should not sell with a green bar, regardless of the zero line. So the AC acts as a permission filter — it tells you whether the underlying force supports the trade direction you are considering.

The zero line and two-bar rules

Position relative to zero adds context. Above zero, momentum is broadly accelerating upward; below zero, downward. Bill Williams specified how many confirming green or red bars are needed depending on which side of zero the AC sits: above zero, two green bars confirm a buy; below zero, more confirmation is required because you would be buying against the prevailing acceleration. This asymmetry reflects that trading with the acceleration is safer than against it.

An early-warning companion, not a standalone

The AC's strength is timing: because it measures acceleration, it changes colour before the AO changes direction and well before price turns, giving an early alert. Its weakness is that early signals are noisy — acceleration flickers, so the AC produces many colour changes, and most are minor. It is designed to be used together with the Awesome Oscillator and the rest of Bill Williams' system, as a confirmation and timing filter, never as a lone trigger.

Formula

Accelerator Oscillator formula

AC = AO − SMA₅(AO), where AO = SMA₅((H+L)/2) − SMA₃₄((H+L)/2)

The AC subtracts a 5-period simple moving average of the Awesome Oscillator from the AO itself. It shares the AO's 5/34 median-price base.

AO — The Awesome Oscillator — 5-period minus 34-period SMA of median price
SMA₅(AO) — 5-period simple moving average of the Awesome Oscillator
AC — Accelerator Oscillator = AO minus its 5-period average
(H+L)/2 — Median price of the bar, the base of the underlying AO

How it is calculated

Compute the Awesome Oscillator: 5-period SMA of median price minus 34-period SMA of median price.
Compute a 5-period simple moving average of the Awesome Oscillator.
Subtract that 5-period AO average from the AO to get the AC value.
Plot as a histogram around zero, colouring bars green when the AC is rising and red when falling.
Read bar colour as the primary signal — green means accelerating, red decelerating — with the zero line for context.

Interpretation & signals

Traders read the AC for acceleration: green bars mean the force behind price is speeding up, red bars slowing down. Bill Williams' rule is not to buy on a red bar or sell on a green one; the zero-line position adds context on which direction the acceleration favours.

Buy / bullish signals

Two consecutive green bars while the AC is above zero, confirming upward acceleration.
The AC turns green (rising) after red bars, signalling momentum beginning to accelerate up.
Below zero, additional green bars build before a buy, since it would be against prevailing acceleration.
Green AC bars confirming a bullish Awesome Oscillator signal.

Sell / bearish signals

Two consecutive red bars while the AC is below zero, confirming downward acceleration.
The AC turns red (falling) after green bars, signalling momentum beginning to decelerate.
Above zero, additional red bars build before a sell, since it would be against prevailing acceleration.
Red AC bars confirming a bearish Awesome Oscillator signal.

False signals to beware

Acceleration flickers, so the AC changes colour often and many signals are minor noise.
In choppy markets the histogram alternates green and red rapidly with no follow-through.
Early acceleration signals can fade before momentum or price actually turns.

Settings, timeframe & conditions

Best settings

5/34 base with a 5-period AO average (Bill Williams default)

Avoid

Trading AC colour changes alone without the AO or trend context

Works best in

Trending markets where acceleration leads clean momentum swings

Struggles in

Choppy ranges where acceleration flickers constantly

Advantages & limitations

Advantages

Signals momentum changes earlier than the AO or price, via acceleration.
Clear green/red colour rule acts as a directional permission filter.
Excellent timing companion to the Awesome Oscillator.
Highlights when a trend's driving force is fading before price confirms.

Limitations & disadvantages

Very noisy — acceleration flickers and produces frequent colour changes.
Early signals often fade before momentum turns.
Unbounded with no fixed overbought/oversold levels.
Not usable alone; needs the AO and a trend framework.

Combining Accelerator Oscillator with other indicators

Awesome Oscillator — The AC measures the acceleration of the AO's momentum — the two are designed to be read together, with the AC giving the earlier timing and the AO the momentum bias.
Moving Average — A trend-defining moving average filters the AC's noisy acceleration signals to those aligned with the larger trend.
Relative Strength Index — RSI adds bounded overbought/oversold context to the AC's early acceleration read, helping confirm exhaustion turns.

Practical examples (Nifty & Bank Nifty)

NIFTY example

Nifty is rallying and the Awesome Oscillator is still rising, but the Accelerator Oscillator has already begun printing red bars — the force behind the advance is decelerating even though momentum is still positive. Following Bill Williams' rule not to buy on a red AC bar, a trader holds off adding longs; the AC's early deceleration warns the up-move is losing its driving force before the AO or price confirms a turn.

BANKNIFTY example

Bank Nifty bottoms and turns up. The Accelerator Oscillator flips to two green bars above zero, confirming upward acceleration, just as the AO crosses zero — the acceleration leads the momentum. A trader takes the green AC bars as permission to act on the bullish AO signal, using Bank Nifty's fast acceleration off the low as an early, confirmed continuation entry.

Common mistakes

Buying on a red bar or selling on a green bar, against Bill Williams' core rule.
Trading every AC colour flicker as a signal in choppy conditions.
Using the AC alone without the Awesome Oscillator or a trend filter.
Ignoring the zero-line context that sets how much confirmation is needed.

Professional usage

Professionals use the Accelerator Oscillator as an early-warning and permission filter within Bill Williams' framework. Because it measures acceleration, it changes before momentum, so they use its colour to decide whether the underlying force supports a trade — never buying on red, never selling on green — and they read the zero line to judge how much confirmation is needed. It is always paired with the Awesome Oscillator and trend structure; its early signals are too noisy to trade in isolation, but its timing edge is valuable for confirming AO signals and flagging fading trends.

Key takeaway

The Accelerator Oscillator measures the acceleration of momentum — whether the force behind price is speeding up or slowing down — by subtracting a 5-period average of the Awesome Oscillator from the AO. Green means accelerating, red decelerating, and Bill Williams' rule is never buy on red or sell on green. It warns earliest of all, but flickers with noise, so use it with the AO and a trend, not alone.

Frequently asked questions

What is the Accelerator Oscillator?

The Accelerator Oscillator, created by Bill Williams, measures the acceleration or deceleration of momentum. It subtracts a 5-period average of the Awesome Oscillator from the Awesome Oscillator itself, plotting the result as a histogram to warn of momentum changes before they reach price.

How is the Accelerator Oscillator calculated?

You first compute the Awesome Oscillator (5-period minus 34-period SMA of median price), then take a 5-period simple moving average of the AO, and subtract it from the AO. The result is the AC, plotted as a green-and-red histogram around zero.

What is the difference between the Accelerator and Awesome Oscillators?

The Awesome Oscillator measures momentum — the force behind price — while the Accelerator Oscillator measures the acceleration of that momentum, its rate of change. The AC changes before the AO, giving an earlier warning of a coming turn.

What do the green and red bars on the Accelerator Oscillator mean?

A green bar means momentum is accelerating; a red bar means it is decelerating. Bar colour is the primary signal: Bill Williams' rule is that you should not buy on a red bar or sell on a green bar, regardless of the zero line.

What is Bill Williams' rule for the Accelerator Oscillator?

His core rule is never to buy when the current bar is red and never to sell when it is green. The AC acts as a permission filter — the colour must support the direction of your intended trade before you act.

What does the Accelerator Oscillator zero line mean?

Above zero, momentum is broadly accelerating upward; below zero, downward. The zero-line position sets how much confirmation is needed — above zero two green bars confirm a buy, while below zero more green bars are required because you would be trading against the prevailing acceleration.

Is the Accelerator Oscillator a leading indicator?

Yes, it is designed to be the earliest of Bill Williams' signals. Because it measures acceleration, which changes before momentum and before price, it gives an early warning — but that speed makes it noisy, so it needs confirmation.

What are the best Accelerator Oscillator settings?

It uses the Awesome Oscillator's 5/34 median-price base with a 5-period average of the AO, following Bill Williams' design. These defaults are rarely changed because the AC's rules are built around them.

Can the Accelerator Oscillator be used for Nifty and Bank Nifty?

Yes. The AC works on any liquid instrument. On Nifty and Bank Nifty its early acceleration signals help confirm Awesome Oscillator entries, though its flickering nature means it should be used with the AO and a trend filter, not alone.

Why does the Accelerator Oscillator give so many signals?

Because acceleration is volatile and flickers, the AC changes colour frequently, producing many signals, most of them minor. This is why it is used as a confirmation and timing filter alongside the Awesome Oscillator rather than as a standalone trigger.

Does the Accelerator Oscillator have overbought and oversold levels?

No. Like the Awesome Oscillator, the AC is unbounded and has no fixed overbought or oversold levels. It is read through bar colour, the zero line and Bill Williams' confirmation rules rather than through set thresholds.

How do you use the Accelerator Oscillator with the Awesome Oscillator?

You use the AO for the momentum bias and the AC for earlier timing and permission. When the AC's colour supports the AO's signal — green for a buy, red for a sell — the combined signal is stronger, which is how Bill Williams intended the pair to work.

Voice search & related questions

Natural-language questions people ask about Accelerator Oscillator.

What is the Accelerator Oscillator in simple words?

It measures whether the force pushing price is speeding up or slowing down. Green bars mean momentum is accelerating, red bars mean it is slowing, giving an early warning before price actually turns.

What is the rule for the Accelerator Oscillator?

Bill Williams' rule is simple: never buy when the bar is red and never sell when the bar is green. The colour has to agree with the direction you want to trade.

How is the Accelerator different from the Awesome Oscillator?

The Awesome Oscillator measures momentum, while the Accelerator measures how fast that momentum is changing. The Accelerator turns before the Awesome Oscillator, so it warns of turns earlier.

Is the Accelerator Oscillator good for early signals?

Yes, it is meant to give the earliest warning of a turn because it measures acceleration, but its signals are noisy, so traders confirm them with the Awesome Oscillator and the trend.

What does a green Accelerator bar mean?

A green bar means the momentum behind price is accelerating. Under Bill Williams' rules, you only consider buying when the current bar is green, not red.

Sources & references

Last reviewed 8 July 2026. Educational content only — not investment advice.