On-balance volume (OBV) is a technical trading momentum indicator that uses volume flow to predict changes in stock price. Joseph Granville first developed the OBV metric in the 1963 book Granville's New Key to Stock Market Profits.
Granville believed that volume was the key force behind markets and designed OBV to project when major moves in the markets would occur based on volume changes. In his book, he described the predictions generated by OBV as "a spring being wound tightly." He believed that when volume increases sharply without a significant change in the stock's price, the price will eventually jump upward or fall downward.
Despite being plotted on a price chart and measured numerically, the actual individual quantitative value of OBV is not relevant. The indicator itself is cumulative, while the time interval remains fixed by a dedicated starting point, meaning the real number value of OBV arbitrarily depends on the start date. Instead, traders and analysts look to the nature of OBV movements over time; the slope of the OBV line carries all of the weight of analysis.
Calculating On-Balance Volume
On-balance volume provides a running total of an asset's trading volume and indicates whether this volume is flowing in or out of a given security or currency pair. The OBV is a cumulative total of volume (positive and negative). There are three rules implemented when calculating the OBV. They are:
If today's closing price is higher than yesterday's closing price, then: Current OBV = Previous OBV + today's volume
If today's closing price is lower than yesterday's closing price, then: Current OBV = Previous OBV - today's volume
If today's closing price equals yesterday's closing price, then: Current OBV = Previous OBV
Limitations of OBV
One limitation of OBV is that it is a leading indicator, meaning that it may produce predictions, but there is little it can say about what has actually happened in terms of the signals it produces. Because of this, it is prone to produce false signals. It can therefore be balanced by lagging indicators. Add a moving average line to the OBV to look for OBV line breakouts; you can confirm a breakout in the price if the OBV indicator makes a concurrent breakout.
Another note of caution in using the OBV is that a large spike in volume on a single day can throw off the indicator for quite a while. For instance, a surprise earnings announcement, being added or removed from an index, or massive institutional block trades can cause the indicator to spike or plummet, but the spike in volume may not be indicative of a trend.
Source: Investopedia, On-Balance Volume (OBV): Definition, Formula, and Uses As Indicator, accessed 27 December 2023, <https://www.investopedia.com/terms/o/onbalancevolume.asp>
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