In short. Cumulative delta is the running sum of each candle's delta from the session open, plotted as a line under the price. It shows whether buyers or sellers have been the aggressors over the session, and it is read for divergence: price making a new high while cumulative delta does not is buying that failed to move price, the classic sign of absorption at the high.
Resetting at the session open keeps the line comparable from day to day. Some traders reset it at the RTH open, others at midnight; the choice changes the picture, so keep one.
Cumulative delta works best with a level: a divergence in the middle of nowhere means little; a divergence at yesterday's high, with absorption visible on the footprint, is a trade with a stop above the high.
Questions traders ask
What is Cumulative delta?
Cumulative delta is the running sum of each candle's delta from the session open, plotted as a line under the price. It shows whether buyers or sellers have been the aggressors over the session, and it is read for divergence: price making a new high while cumulative delta does not is buying that failed to move price, the classic sign of absorption at the high.