Defining Range

What is a Defining Range?

A defining range (DR) is a fixed one-hour window whose extremes become the reference frame for the rest of a trading session. The framework, popularized in index-futures day-trading communities, marks two ranges from that hour: the DR proper, the full high-to-low including wicks, and inside it the implied defining range (IDR), drawn from the highest and lowest candle bodies with wicks excluded. The most-watched window is the first hour of the New York regular session, 9:30 to 10:30 New York time, with overnight and Asian-session counterparts defined the same way in other trading sessions.

Once the hour completes, the framework turns directional: a close beyond the IDR high or low (commonly a five-minute close) confirms the session bias, and the working assumption is that the opposite extreme of the range then holds for the remainder of that session. That assumption is statistical, drawn from community backtests rather than any mechanical necessity, and it fails on reversal days, so the levels function as bias plus invalidation rather than a standalone signal. In spirit it is a body-refined cousin of the classic opening range breakout.

How traders use it

• As a session bias filter: after the defining hour ends, a confirmed close above the IDR high biases the session long and a close below the IDR low biases it short, with the opposite DR extreme acting as the invalidation line.
• As an intraday level set: the DR and IDR highs, lows, and midpoint serve as retest levels for entries, and the DR's height is projected above and below in half-range steps (in the spirit of standard-deviation projections) to frame targets.
• As a per-session reset: separate defining ranges for the Asian, overnight, and regular sessions let the bias re-anchor several times a day instead of carrying one read across the full 24-hour cycle.