Prior day high and low, and why they get respected
There is nothing special about yesterday’s extremes except that everyone can compute them the same way. That turns out to be enough.
Yesterday's high and low come up constantly, and the reason is unglamorous: they are unambiguous. No settings, no smoothing, no interpretation. Every participant looking at the instrument arrives at the same two numbers.
Compare that to a moving average, where one trader's 20-period and another's 50-period sit in different places, or a trendline, where two people drawing from the same chart produce two different lines. Prior day levels have none of that ambiguity, so attention concentrates on them.
The mechanism
Yesterday's high is where buying stopped being enough. Somebody was willing to sell there in size. Traders who wanted to sell and missed remember the level. Traders who bought near it and watched price fall have a breakeven in mind. Stops sit above it for anyone short.
The level is not doing anything. It is a coordination point — the same effect that makes round numbers matter, for equally unsophisticated reasons.
Related levels worth marking
- Prior close or settlement — the last agreed price, and the reference for daily change on every quote screen
- Today's open — splits the session into above and below where it started
- Overnight high and low — for instruments that trade outside regular hours
- Prior week's extremes — the same logic at a slower cadence
A definitional trap on futures. “Yesterday's high” depends entirely on what counts as yesterday. Regular hours only, or the full overnight session? Exchange settlement time or midnight? Different chart settings produce different levels, and it is common for two traders to be watching genuinely different numbers while using the same phrase. Decide which you mean and keep it consistent.
What actually happens at them
Two outcomes, and the level does not tell you which. Price approaches, meets enough resting supply, and turns. Or it approaches, consumes what is resting, and accelerates as stops trigger — the same concentration of orders that can hold a level is what makes a break move quickly.
The concentration causes both. Knowing the level tells you where something is likely to happen. It does not tell you what.
Why they are still worth marking
Because they narrow attention. On a chart with hundreds of prices, a small number where activity is more likely is genuinely useful — and unlike most levels, these are chosen by a rule that cannot be fitted after the fact. You could have drawn them before the session opened, which is more than can be said for most lines on most charts.