On Balance Volume (OBV): Reading the Flow

Price tells you what happened. Volume tells you how much conviction was behind it. On balance volume OBV is the cleanest way to fold those two together into a single running line, and it has been doing the job since Joe Granville popularized it in the 1960s. The idea behind it is almost stubbornly simple, which is exactly why it still works.

Granville's bet was that volume moves before price. Smart money accumulates a stock quietly, and that buying shows up in volume well before the price chart makes it obvious. OBV is his attempt to make that hidden flow visible.

How OBV Is Calculated

The math fits on a napkin. OBV is a running total of volume, where each day's volume is either added or subtracted based on the close.

• If today's close is higher than yesterday's, add today's volume to the running total.
• If today's close is lower than yesterday's, subtract today's volume.
• If the close is unchanged, the OBV stays flat.

That is the whole formula. The result is a line that climbs when volume is flowing in on up days and falls when volume is flowing out on down days.

The Core Read: Confirmation

The first job of OBV is to confirm a price move. In a healthy uptrend, you want OBV making higher highs right alongside price. That tells you the rally has real volume behind it. Buyers are showing up in size on the up days, and the move has fuel.

The same logic runs in reverse. In a downtrend, OBV making lower lows with price confirms that selling pressure is genuine. When price and OBV move together, the trend has the participation it needs to keep going. There is no surprise in the tape.

The Powerful Part: Divergence

Confirmation is useful, but divergence is where OBV earns its reputation. Divergence happens when price and OBV disagree, and it often shows up before a turn in price.

A bullish divergence is the classic accumulation signal Granville was hunting for. Price is grinding to new lows, retail traders are giving up, but OBV quietly refuses to make a new low because someone is soaking up shares on the down days. That mismatch is the footprint of a buyer who knows something.

Using OBV With Trendlines

Here is a trick that sharpens the indicator. You can draw trendlines directly on the OBV line itself, the same way you would on price. A break of an OBV trendline often leads a break on the price chart. If OBV slices below a rising support line it has respected for weeks, that shift in flow can be your heads-up that price is about to follow.

Some traders watch only the OBV trendline and treat the price chart as the confirmation, flipping the usual order of operations. It works because volume is the cause and price is the effect.

Common Mistakes

Reading the raw number

New users see OBV at negative 50 million and panic. The starting value is arbitrary. Slope and direction are all that count, never the absolute figure.

Trading divergence as a signal by itself

Divergence can run for weeks while price keeps climbing. Acting on it alone gets you short into a trend that has not finished. Use it to get alert, then wait for price to break.

Ignoring that close-only is blunt

OBV counts the entire day's volume as buying or selling based on a single tick, the close versus the prior close. A day that ranged wildly but closed up one cent counts as fully bullish. It is a coarse measure, so do not expect surgical precision.

Using it on illiquid names

On thin, low-volume stocks, a single large print can yank OBV around and produce false signals. The indicator behaves best on liquid names with steady, meaningful volume.

Spotting Volume Divergence Faster

Divergence is easy to see in a textbook and easy to miss in the wild. You have to compare the swing highs and lows on price against the matching points on OBV, across every chart you follow, and the disagreements are often subtle until they suddenly are not.

ChartRead reads a chart screenshot and flags where volume is supporting a move or quietly pulling away from it, alongside the structure on price, so you can catch the names where flow and price have started to part ways.