The Accelerator Oscillator is Bill Williams’s companion to the Awesome Oscillator. Where AO measures the difference between momentum (5-period and 34-period SMA of median price), AC measures the rate of change of that momentum — in physics terms, AO is velocity and AC is acceleration. AC fires earlier than AO because acceleration leads velocity changes.
In Williams’s original framework, AC is a confirmation tool used alongside AO. The “three bars” entry rule — three consecutive same-colour AC bars — provides earlier trade triggers than waiting for AO’s saucer or zero-line cross.
What is the Accelerator Oscillator?
AC is calculated by taking AO (the difference between 5-SMA and 34-SMA of median price), then subtracting a 5-period SMA of AO from AO itself. The result oscillates around zero with green bars (current value above previous) and red bars (below previous), same colour logic as AO.
The math captures momentum’s second derivative. When AO is rising at an increasing rate, AC is positive and rising. When AO is rising but at a decreasing rate (i.e., approaching a peak), AC is positive but falling. AC turning negative often precedes AO’s zero-line cross.
How AC Works on MT4
AC is built into MT4: Insert > Indicators > Bill Williams > Accelerator Oscillator.
Williams’s primary signal is the three-bars rule:
For a long trade above zero: three consecutive green bars all above zero. AC is accelerating upward in already-positive territory.
For a short trade below zero: three consecutive red bars all below zero. AC is accelerating downward in already-negative territory.
For a long trade below zero (counter-trend): three consecutive green bars while AC is still below zero. Early-warning of upward momentum starting.
For a short trade above zero: three consecutive red bars while AC is still above zero. Early-warning of downward momentum starting.
The first two cases (with-trend signals) are higher-probability. The latter two (counter-trend early warnings) are lower-probability but catch turns earlier.
Key Features
- Built into MT4 – Insert > Indicators > Bill Williams > Accelerator Oscillator
- Histogram visualisation with green/red bars
- Measures momentum acceleration (AO’s rate of change)
- Faster than AO – earlier trade triggers
- Non-repainting once candles close
- Default settings (5/34 SMA on median price) work universally
Best Settings for AC
Like AO, AC’s defaults are what 95% of traders use. Don’t tweak.
| Parameter | Default (recommended) |
|---|---|
| AO Fast Period | 5 |
| AO Slow Period | 34 |
| AC Smoothing Period | 5 |
| Applied Price | Median Price (H+L)/2 |
Recommended starting point: Defaults on H1 and H4. Like AO, AC produces too much noise on M5 and below.
Pros and Cons
| Pros | Cons |
|---|---|
| Faster than AO – catches momentum changes earlier | More false signals than AO due to higher sensitivity |
| Built into MT4, non-repainting, easy to use | Requires AO context to interpret correctly |
| Three-bars rule is unambiguous and easy to backtest | Counter-trend early-warning signals fail more often than they succeed |
| Pairs naturally with AO and Alligator in Bill Williams’s framework | Standalone use is limited – it’s a confirmation tool |
How to Install AC on MT4
Step 1: Open MT4 and select your chart.
Step 2: Click Insert > Indicators > Bill Williams > Accelerator Oscillator.
Step 3: Default settings. Pick contrasting colours for green/red bars.
Step 4: Click OK. Save as a template alongside AO and Alligator if you trade Bill Williams’s framework.
Trading Strategy: AC Three-Bars Rule
Setup: AC with default settings, AO on the same chart, Alligator on price for trend context.
Buy Signal (with trend, above zero):
1. Alligator confirms uptrend (jaw, teeth, lips aligned upward)
2. AO is above zero
3. AC prints three consecutive green bars all above zero
4. Enter long on the close of the third bar
Sell Signal (with trend, below zero):
1. Alligator confirms downtrend
2. AO is below zero
3. AC prints three consecutive red bars all below zero
4. Enter short on the close of the third bar
Stop Loss: Beyond the recent swing extreme.
Take Profit: Trail until AC prints two consecutive opposite-colour bars.
The three-bars rule with all the contextual filters (Alligator, AO position) is what separates this from random AC entries. Skip any of those filters and the win rate drops significantly.
Frequently Asked Questions
Is the AC indicator free?
Yes. Built into MT4 and the enhanced version below is also free.
Does AC repaint?
No.
AC vs AO – which is better?
They’re complementary tools, not alternatives. AC measures acceleration, AO measures momentum. AC fires earlier; AO confirms. Use both together in Williams’s framework.
Best timeframe for AC?
H1 and H4 same as AO. M5/M15 is too noisy.
Can I use AC on MT5?
Yes. Built into MT5 with identical behaviour.
Download Enhanced AC Indicator for MT4 – Free
- Multi-timeframe display
- Three-bars pattern alerts
- Zero-line cross alerts
Platform: MT4 (Build 1000+)
File type: .ex4
File size: 13 KB
Version: 2.0
Last updated: April 2026
Download the Accelerator Oscillator – Free Instant Access
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- The non-repainting Accelerator Oscillator file (.ex4)
- Step-by-step installation guide
- Bill Williams’s full Accelerator Oscillator framework explained
- The exact three-bars entry rules I use in live trading
- Weekly trading insights from a developer with 16+ years of market experience
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- The non-repainting Accelerator Oscillator Indicator file (.ex4) – install in 30 seconds
- Step-by-step installation guide with chart screenshots
- Best-performing settings for scalping, day trading, and swing trading
- The exact entry and exit rules Dom uses in live trading
- Weekly trading insights from a developer with 16+ years of market experience
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Overall Rating: 4.2/5
| Category | Rating |
|---|---|
| Accuracy | 4.1/5 |
| Ease of Use | 4.4/5 |
| Features | 4.0/5 |
| Value | 4.3/5 |
Related Indicators
- Awesome Oscillator MT4 – The momentum companion to AC
- Alligator Indicator MT4 – Bill Williams’s trend identification tool
- Best Oscillator Indicators for MT4
- How to Install Custom Indicators on MT4
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