High/Low Index: Smoothing New Highs vs New Lows

Key Takeaways

• High/Low Index equals the 10-day SMA of Record High Percent, where Record High Percent is new highs divided by new highs plus new lows.
• The 50 line separates bullish from bearish breadth; sustained readings above 70 reflect persistent leadership strength.
• Investors who use the index without context mistake any cross of 50 for a signal and get whipsawed in choppy markets.
• StockCharts publishes the index for major US indices and for each of the eleven S&P sector SPDR ETFs.

What It Is

Record High Percent is a one-day breadth statistic that ignores unchanged issues and simply asks: among the stocks making fresh 52-week highs and fresh 52-week lows today, what share are highs? The High/Low Index applies a 10-day simple moving average to that daily ratio. The smoothing removes the daily noise and produces a series suitable for trend analysis.

The reading lives on a [0, 100] scale. Because it is symmetric around 50, the same chart works for both bullish and bearish regimes. New highs are not a deep input; it is a count of stocks at extremes. That is precisely why it works as a leadership gauge.

The Intuition

In a healthy bull market many stocks reach new yearly highs and few reach new lows. Record High Percent prints near 100 every day, and its 10-day average pins above 70. That is what wide participation looks like.

When the leadership narrows, you see a peculiar pattern: the index can still rise, but Record High Percent dips below 50 because as many names are making new lows as new highs. The High/Low Index falls below 50 and stays there until breadth heals or capitulation hits.

How It Works

The formulas are:

Record High Percent = 100 * (New 52-week Highs) / (New 52-week Highs + New 52-week Lows)
High/Low Index = 10-day SMA of Record High Percent

Interpretation rules used by ChartSchool and most institutional desks:

• Above 70: strong, persistent leadership. Bullish bias.
• 50 to 70: bullish bias with mixed leadership.
• 30 to 50: bearish bias with weakening internals.
• Below 30: persistent leadership on the downside. Bearish.

Crosses through 50 mark regime shifts but only when the move sustains for more than a few days. Divergences between the index and price are the strongest signal: a new price high paired with a falling High/Low Index is a classic narrowing-leadership warning.

Worked Example

Suppose for ten consecutive trading days the count of new highs and new lows on the S&P 500 looks like this:

• Days 1 to 5: 80 highs, 5 lows daily. RHP = 80/85 = 94.1.
• Days 6 to 10: 30 highs, 25 lows daily. RHP = 30/55 = 54.5.

The 10-day SMA equals (5 * 94.1 + 5 * 54.5) / 10 = 74.3. The High/Low Index reads 74.3, comfortably above 70.

Now suppose for the next ten days, the counts shift to 10 highs and 40 lows daily. RHP collapses to 10/50 = 20. The 10-day SMA drops sharply as the older 94.1 prints roll out. Within a week the High/Low Index crosses below 50, then below 30, signaling a broad shift in market character.

Common Mistakes

1. Ignoring the universe size. A sector with 30 stocks moves the indicator on much smaller flow than the S&P 500. Compare High/Low Index readings only within the same universe.
2. Reading short-term crosses as triggers. The smoothing already includes 10 days. Trade the trend of the index, not single-day crosses.
3. Mixing 52-week highs with shorter-window highs. Some platforms offer 20-day or 252-day versions; their dynamics differ.
4. Forgetting that the index ignores neutral days. If 5 stocks make new highs and 5 make new lows, RHP equals 50 regardless of whether the index is up 2 percent or down 2 percent.
5. Treating it as a timing oscillator. It is not bounded like RSI; values can stay above 70 or below 30 for months in strong trends.

Frequently Asked Questions

What is the high low index in simple terms? It is a 10-day moving average of the share of stocks making fresh 52-week highs versus those making fresh 52-week lows. Above 50 means highs are winning; below 50 means lows are winning.

How does the high low index affect investment decisions? Investors use it to confirm or question the breadth of a rally. Sustained readings above 70 indicate broad leadership and support a fully invested posture; readings below 30 suggest narrow, weak markets that deserve defense.

What is a real-world example of the high low index? In strong bull runs such as 2017 the S&P 500 High/Low Index spent most of the year above 70. Late in 2018 it dropped below 30 within weeks as new lows accumulated, marking the regime shift before the index found a bottom.

How can investors use the high low index effectively? Watch the trend of the index more than its absolute level, pay attention to divergences with the underlying price index, and use sector versions to identify leadership rotation early.

How is the high low index different from the McClellan Oscillator? McClellan smooths net advancing issues with two EMAs and lives on a +/-100 scale. The High/Low Index smooths new highs versus new lows with a single SMA and sits between 0 and 100. They measure different breadth dimensions.

Sources

1. StockCharts ChartSchool. High-Low Index. https://chartschool.stockcharts.com/table-of-contents/market-indicators/high-low-index
2. StockCharts ChartSchool. Record High Percent. https://chartschool.stockcharts.com/table-of-contents/market-indicators/record-high-percent
3. StockCharts ChartSchool. StockCharts High-Low Index. https://chartschool.stockcharts.com/table-of-contents/index-and-market-indicator-catalog/stockcharts-high-low-index
4. StockCharts ChartSchool. High-Low Percent. https://chartschool.stockcharts.com/table-of-contents/market-indicators/high-low-percent

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.