PDH (also PDL etc. – see also OHLC)

PDH stands for "previous day's high" — the highest price a stock, future, or other instrument traded during the last completed trading session. Its counterpart, PDL, is the "previous day's low" — the lowest price traded that same session. Traders use these two levels constantly as quick reference points on a chart, often marked as horizontal lines.

The idea behind watching PDH and PDL is that price tends to react to levels where it previously found buyers or sellers in size. If yesterday's high was $52.10, that price stands out today as a spot where sellers showed up before, so it becomes a level to watch for either a breakout (price pushes through and keeps going) or a rejection (price touches it and turns back down). The same logic applies to PDL, but for buying interest that showed up at a low point.

The nuance that trips people up is defining "previous day." For instruments that trade nearly around the clock, like futures or crypto, "previous day" depends on which session boundaries you're using — the exchange's official session, the regular stock market hours, or a 24-hour clock. A stock's previous day is usually straightforward, running from the prior regular session's open to close, but pre-market and after-hours trades can shift the number depending on whether your charting platform includes them. Always check what your data feed counts as "the day."

PDH and PDL are two of the four numbers that make up OHLC (open, high, low, close) for a given session, so learning one naturally leads to the others.