McClellan Oscillator: Net Advances Breadth Signal

Key Takeaways

• McClellan oscillator equals the 19-day EMA of advances minus declines minus the 39-day EMA of the same series.
• Positive readings mean breadth is improving; negative readings mean broad participation is weakening even when the index holds up.
• A breadth thrust, a fast move from below -50 to above +50, often marks the start of a sustained advance.
• Divergence between the oscillator and the price index is one of the most reliable signs of an exhausted trend.

What It Is

The McClellan oscillator is a single oscillating line that crosses around zero. It is computed on the breadth data of an exchange, classically the NYSE, by smoothing the daily net advances series with two exponential moving averages and subtracting one from the other.

It is read alongside the index it covers. The oscillator does not predict price by itself; it measures whether the underlying participation is strengthening or weakening.

The Intuition

A stock index can rise while fewer and fewer of its members participate. This happens when a small number of large-cap names carry the tape and the average stock is already weak. The reverse can happen near bottoms, where the index keeps making new lows but more stocks stop going down.

Net advances captures that participation directly: it is the number of stocks up on the day minus the number down. Smoothing it with a fast and a slow EMA, then taking the difference, gives a momentum line on the breadth series. That line picks up changes in participation before the index notices.

How It Works

The classic formula uses the 19-day and 39-day exponential moving averages, which correspond to smoothing constants of 0.10 and 0.05:

NetAdv_t      = AdvancingIssues_t - DecliningIssues_t
EMA19_t       = EMA19_t-1 + 0.10 * (NetAdv_t - EMA19_t-1)
EMA39_t       = EMA39_t-1 + 0.05 * (NetAdv_t - EMA39_t-1)
McClellanOsc  = EMA19_t - EMA39_t

A reading above zero means the fast EMA of net advances is above the slow one; advancing issues are gaining the upper hand. A reading below zero says declines are dominating.

Typical readings sit roughly between -100 and +100. Levels beyond +50 or -50 are considered stretched, although extremes can stay elevated for short stretches at the start of strong trends. The McClellans also publish a ratio-adjusted version that scales net advances by the sum of advances plus declines, which makes the indicator comparable across decades as the total number of NYSE issues changes.

The summation index, a running cumulative total of the oscillator, is treated as a separate but related tool for longer-term timing.

Worked Example

Suppose yesterday's EMA19 of net advances on the NYSE was +80 and yesterday's EMA39 was +30, giving a McClellan oscillator value of +50. Today the exchange reports 2,000 advancers and 1,200 decliners, so net advances are +800.

EMA19_today = 80  + 0.10 * (800 - 80)  = 80  + 72  = 152
EMA39_today = 30  + 0.05 * (800 - 30)  = 30  + 38.5 = 68.5
McClellanOsc_today = 152 - 68.5 = 83.5

The oscillator has jumped from +50 to +83.5 on one strong breadth day. A series of similar days that lifts the line from below -50 to above +50 in a short window is the classic breadth thrust, often associated with the start of a multi-month advance.

If the next session prints 1,200 advancers and 2,000 decliners, net advances flip to -800 and both EMAs reset materially:

EMA19 = 152 + 0.10 * (-800 - 152) = 152 - 95.2 = 56.8
EMA39 = 68.5 + 0.05 * (-800 - 68.5) = 68.5 - 43.4 = 25.1
McClellanOsc = 56.8 - 25.1 = 31.7

The oscillator pulls back to +31.7 after a single bad breadth day.

Common Mistakes

1. Using the wrong breadth universe. The classic indicator is built on NYSE issues. Applying it to Nasdaq raw counts without ratio-adjustment can produce systematic bias because the listing mix is different.

2. Trading every zero cross. Crossings are frequent and many are noise. Use the oscillator alongside the trend of the price index and the summation index, not as a stand-alone trigger.

3. Ignoring divergences. When the index makes a new high but the oscillator does not, breadth is failing. That is one of the strongest signals the indicator produces, and it is often ignored because it goes against the headline tape.

4. Confusing scale with strength. Modern NYSE listings include many ETFs and preferreds. Raw net advances can produce wider swings than they did decades ago. Use a ratio-adjusted version or rescale before comparing across eras.

5. Treating extremes as automatic reversals. Readings beyond plus or minus 100 can hold during strong starts of trends. Pair extremes with a confirming pattern before fading them.

Frequently Asked Questions

What is the McClellan oscillator in simple terms? The McClellan oscillator measures how many more stocks are going up than down on the NYSE, smoothed over short and long windows. It tells you whether the average stock supports the index move.

How does the McClellan oscillator affect investment decisions? Strong breadth thrusts often confirm new bull legs and help investors stay long. Divergences warn that an apparently strong index is being carried by a shrinking group of leaders.

What is a real-world example of the McClellan oscillator? Market technicians watch the NYSE McClellan oscillator daily on services like StockCharts. After the March 2020 low, the oscillator produced an unusually strong breadth thrust that confirmed the start of a sustained recovery.

How can investors use the McClellan oscillator effectively? Read it alongside the price index and the McClellan summation index. Use thrusts and divergences as conviction adjustments rather than as primary entry signals.

How is the McClellan oscillator different from the advance-decline line? The advance-decline line is a cumulative breadth total. The McClellan oscillator is a momentum reading on that same breadth, so it turns earlier and oscillates around zero instead of trending.

Sources

1. McClellan Financial Publications. "The McClellan Oscillator." https://www.mcoscillator.com/learning_center/kb/mcclellan_oscillator/
2. StockCharts ChartSchool. "McClellan Oscillator." https://chartschool.stockcharts.com/table-of-contents/market-indicators/mcclellan-oscillator
3. American Association of Individual Investors. "McClellan Oscillator." https://www.aaii.com/journal/article/technicallyspeaking-mcClellan-oscillator
4. McClellan Financial Publications. "The McClellan Oscillator and Summation Index." https://www.mcoscillator.com/learning_center/kb/mcclellan_oscillator/the_mcclellan_oscillator_summation_index/

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.