What ATR actually is
ATR, short for Average True Range, is a volatility indicator created by J. Welles Wilder, the same trader who gave us the RSI. It answers one question: how much does this instrument typically move over a given period. The default lookback is 14 bars, so on a daily chart a 14-period ATR is roughly the average daily range over the last two weeks of trading.
The key thing to hold onto is what ATR does not do. It says nothing about direction. A high ATR does not mean a stock is going up or down, only that it is moving a lot in whichever direction it happens to move. ATR measures the size of the swings, full stop. That is exactly what makes it useful, because size is the input you need for stops and sizing, and it is a question direction indicators cannot answer.
How True Range is calculated
Before you can average anything, you need the True Range of a single bar. True Range is the largest of these three numbers:
- 1. High minus low = current high − current low. The plain range of this bar.
- 2. High minus prior close = absolute value of current high − previous close. Catches a gap up.
- 3. Low minus prior close = absolute value of current low − previous close. Catches a gap down.
ATR is then simply the moving average of the True Range over the lookback, 14 by default. The reason Wilder reached back to the previous close, rather than just taking high minus low, is gaps. If a stock closes at $50 and opens the next day at $46 after bad news, the plain high-minus-low of that new bar might look small and calm, while the real move from the prior close was $4. Using the previous close captures that overnight jump, so ATR reflects the true distance price traveled, not just the distance inside a single session.
What high versus low ATR means
A high ATR means a volatile, fast-moving instrument that covers a lot of ground each bar. A low ATR means a calm, quiet one that barely budges. Neither is good or bad on its own, they just call for different handling: a volatile name needs wider stops and a smaller position, a quiet one can take a tighter stop and a larger size for the same dollar risk.
The one trap is reading ATR in raw dollars without the price. A $2 ATR on a $50 stock is a typical move of 4%, which is a lively stock. A $2 ATR on a $500 stock is under half a percent, which is practically asleep. Same $2, wildly different volatility. When you want to compare one name to another, read ATR as a percent of price, not as a dollar figure, or you will mistake expensive stocks for volatile ones.
The three ways to use it
ATR earns its keep in three places, and all three come back to giving a trade the right amount of room.
Stop placement. Instead of a round-number stop, set your stop a multiple of ATR away from entry, often 1.5x or 2x. If ATR is $2 and you use a 2x stop, you place it $4 back. That distance is tuned to the stock’s own normal movement, so ordinary noise does not clip you out of a trade that was never actually wrong.
Position sizing. A wider ATR means a wider stop, and a wider stop means fewer shares for the same fixed dollar risk. This is the link most traders miss. Once you size off an ATR-based stop, the volatile stock automatically gets a smaller position and the calm one a larger position, and your risk per trade stays constant across both.
Targets. Because ATR tells you how far price tends to travel, you can project realistic move sizes with it. A target one or two ATRs from entry is grounded in what the stock actually does, rather than a hopeful round number the stock has no history of reaching in your timeframe.
Why ATR is an input, not a signal
Here is the mental model that keeps ATR useful: it is an input, not a signal. It never tells you to buy or sell. It tells you how much room to give a trade and how big to size it once you have decided, on your own, to take that trade. Direction comes from your setup, your levels, your read of the tape. ATR then answers the follow-up question every good plan asks, which is how much space and how many shares. Ask it that question and it is one of the best tools you have. Ask it which way to trade and it has nothing to say.