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.

The framework is recent and community-born, generally credited to the futures trader known online as TheMas7er, who released it in 2022 after backtesting index-futures sessions; it spread through indicator implementations rather than books. Common implementations mark three windows a day: a regular-session DR (RDR) over the first hour of regular trading hours, an overnight DR (ODR) in the London morning, and an Asian DR (ADR), each governing only its own session. The method is a schedule of resets, closer to other intraday time-of-day effects than to pattern analysis.

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.

The appeal is procedural: identical clock windows every day produce levels that exist before any trade is considered, which makes preparation and journaling easier. The limits are those of any fixed-clock construct: daylight-saving shifts move the windows against some exchanges, thin holiday sessions produce small ranges whose breaks mean little, and releases on macro event days routinely run through both extremes, exactly the reversal-day failure the invalidation level caps. It also says nothing about higher-timeframe direction, so many users frame it inside a bias derived elsewhere.

How to Mark a Defining Range on a Chart

On a 5-minute chart of an index future, the framework's home market, the construction is mechanical:

1. 1Mark the session window, for example 9:30 to 10:30 New York time, and let it complete; nothing is drawn from a partial hour.
2. 2Draw the DR: horizontal lines at the window's absolute high and low, wicks included.
3. 3Draw the IDR inside it: lines at the highest and lowest candle bodies (opens or closes) of the same window.
4. 4After the hour ends, wait for a 5-minute close outside the IDR; that close sets the session bias, long above or short below.
5. 5Treat the opposite DR extreme as the invalidation line for that bias, and log whether it held.

How it's calculated

Fixes the high/low range (DR) and body-only range (IDR) of one set session hour, then projects multiples of the IDR height as levels for the rest of the session.

Standard windows in the DR/IDR framework, all New York time: regular session 09:30 to 10:30, overnight 03:00 to 04:00, afternoon 19:30 to 20:30.

The projections are conventionally called standard deviations but are fixed multiples of the range, not statistical deviations; they only apply after the window closes and are tracked until the session ends.

Some implementations project multiples of the DR height or anchor the levels at the DR extremes instead.

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 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.
• As an event-day filter: on CPI, Fed, and similar release days many DR traders stand aside, since news candles routinely take both extremes and void the one-side assumption.
• As a statistics project: logging how often the opposite extreme holds, per instrument and session, in the spirit of session high/low statistics, turns a borrowed rule into a measured one; the log doubles as a journal tag alongside day-of-week effects.

Defining Range vs Related Session Frameworks