The Average True Range (ATR) is a deceptively simple indicator that solves one of trading's most practical problems: how much can you expect a stock to move, and how should you size your position and place your stops accordingly? Unlike indicators that try to predict direction, ATR measures volatility—the actual price movement in a stock. Understanding and using ATR properly can dramatically improve your risk management, stop loss placement, and position sizing on FTSE stocks. In this guide, we'll explore what ATR is, how to calculate it, and how to apply it across different trading scenarios.
What Is ATR and How It's Calculated
ATR stands for Average True Range. It measures the average distance price moves in a given period, taking into account gaps. The calculation is a two-step process.
Step 1: Calculate True Range. True Range is the greatest of three values: (1) the distance from the high to the low of the current period, (2) the distance from the prior close to the current high, or (3) the distance from the prior close to the current low. In other words, you're capturing the full range of price movement, including any gap from the previous close.
Why measure this way? Because it accounts for gaps. If a FTSE 100 stock closes at 150p and gaps up to 160p at the open, the gap from close to open is important information. A simple high-low range would miss it. True Range captures it.
Step 2: Average True Range. ATR is typically a 14-period average of True Range. You calculate the True Range for each of 14 periods and then average them. That's your ATR. As new periods form, the oldest period drops off and a new one is added, so ATR updates continuously.
The practical result: ATR gives you a single number that represents the typical daily (or period) volatility. A stock with an ATR of 3p is moving 3p per period on average. A stock with an ATR of 15p is moving 15p per period. Knowing this number is incredibly useful for position sizing and risk management.
True Range vs Average True Range
It's worth understanding the distinction, even though you'll primarily use ATR in trading.
True Range is the raw daily movement—the actual range for a single period. It varies wildly from day to day. On a quiet day, a stock might have a 2p True Range. On an earnings announcement day, it might spike to 20p. These swings are normal.
ATR smooths this out. By averaging the True Range over 14 periods, you get a reading that's stable enough to use for decision-making, but still responsive to changes in volatility. If volatility increases over several days, ATR rises. If it decreases over several days, ATR falls. It's adaptive.
The key insight: True Range is noise; ATR is signal. You use ATR, not individual True Range readings, for your trading calculations.
Reading ATR Values: What High and Low ATR Tells You
ATR is always relative. There's no absolute number that means "high volatility" across all stocks. Instead, you compare a stock's current ATR to its own historical range, or you compare similar stocks to each other.
High ATR: Relative to a stock's recent history, a high ATR means volatility has expanded. Price is making bigger daily moves. For a stable FTSE 100 stock like Rolls-Royce, an ATR of 8p might be high (compared to its usual 2-3p). For a volatile stock like a junior explorer, 8p might be low. You evaluate in context.
High ATR creates both opportunity and risk. Bigger moves mean bigger potential profits, but also bigger potential losses. You may need to reduce position size when ATR is high, or increase stops. Conversely, some traders like trading when ATR expands because it creates tradeable moves.
Low ATR: Relative to a stock's recent history, a low ATR means volatility has compressed. Price is making smaller daily moves. A stock that usually moves 4p is now moving 1-2p. This is the calm before the storm.
Low ATR presents its own opportunities. It often precedes breakouts (similar to the Bollinger Squeeze we discussed in the bands article). When volatility is this compressed, big moves are coming. Traders anticipate this and position for breakouts.
Practical reading: Look at a 1-year chart of a FTSE 250 stock like Barratt Developments. Find periods when ATR was at multi-year lows (high compression, tight trading). Notice what happened next—usually a sharp move in one direction. Compare that to periods when ATR was elevated (high volatility expansion). You'll see the stock made bigger swings, but less predictable ones. Knowing this shapes your trading strategy.
ATR for Stop Loss Placement
This is the most practical use of ATR for most traders. Instead of placing stops at arbitrary round numbers or a fixed distance from entry, you use ATR to place stops that account for normal volatility.
The 1.5x ATR method: Calculate 1.5 times the current ATR and place your stop that distance away from your entry. If you're buying a stock and ATR is 2p, your stop would be 3p (1.5 × 2) below your entry. This allows for normal volatility noise while keeping you out if the trade is genuinely wrong.
The 2x ATR method: More conservative traders use 2 times ATR. With the same 2p ATR, the stop would be 4p away. This gives the trade more room to breathe and is useful if you're trading a more volatile stock or if you want to give your thesis more time to play out.
Practical example: You're buying Shell (FTSE 100) at 2600p. Current ATR is 8p. Using the 2x ATR method, your stop loss is 2600p - (2 × 8p) = 2584p. This stop is logical because it accounts for Shell's normal daily volatility. Losing 16p per share is acceptable; if price drops more than that, something is wrong with your thesis.
The beauty of ATR-based stops is they're not arbitrary. You're not thinking, "I'll put my stop 20 points away because that feels safe." You're basing it on what the stock actually does. This is objective risk management.
Adjust the multiplier (1.5x vs 2x) based on your risk tolerance and the timeframe. Shorter timeframes allow tighter stops (1.5x); longer timeframes benefit from wider stops (2x or 2.5x). You're trying to give your trade room for normal noise while cutting losses when it's genuinely wrong.
ATR for Position Sizing
Proper position sizing is the bedrock of profitable trading, and ATR helps you size positions based on actual risk.
The formula: Determine the maximum amount you want to risk per trade (say, £500 or 2% of your account). Divide that by your stop loss distance (in pounds). That's your position size.
Example: Your account is £25,000 and you risk 2% = £500 maximum loss per trade. You're buying Shell at 2600p with a 2x ATR stop at 2584p. Your risk per share is 16p. To risk £500, you can buy £500 ÷ £0.16 per share = 3,125 shares (roughly). Adjust for your specific account size and risk parameters.
Without ATR, you might arbitrarily decide to buy "1,000 shares." But 1,000 shares with a 16p stop is very different risk than 1,000 shares with a 4p stop (on a less volatile day). ATR-based sizing normalizes this. You're always risking approximately the same amount per trade, regardless of the stock's current volatility.
This is crucial for long-term profitability. If you're risking different amounts on every trade, your wins and losses are inconsistent. But if you're always risking a fixed percentage per trade, your risk is standardized and your compounding is predictable.
ATR for Identifying Breakout Potential
Stocks with expanding ATR are prime candidates for breakouts. When volatility begins to increase, it signals that price is about to make a decisive move.
The setup: Identify a stock in a range (trading between support and resistance levels). Monitor the ATR. If ATR is compressing to 6-month or 12-month lows, a breakout is likely. When ATR begins to expand (rising for 3-5 consecutive periods), the breakout is starting.
When ATR expansion coincides with price breaking above resistance or below support, that's a confirmation signal. The breakout is real and likely to continue.
Practical example: A FTSE 250 stock like Taylor Wimpey has been trading in a 200p-220p range for 3 months. ATR has been low, around 1.5p. Then over a week, ATR starts climbing: 1.5p, 2p, 2.5p, 3.5p, 5p. Meanwhile, price breaks above 220p on volume. The ATR expansion is telling you volatility is surging, which means the breakout is legitimate and not just a false poke. You can size up on this trade with confidence.
This application works across all timeframes. On 4-hour charts, when ATR expands, intraday breakouts are likely. On daily charts, when ATR expands, multi-day or multi-week moves are likely. The logic is consistent: expansion of volatility precedes significant moves.
ATR Trailing Stops (Chandelier Exit)
The Chandelier Exit is a advanced application of ATR that creates dynamic trailing stops. Instead of a fixed stop distance, your stop moves based on ATR.
How it works: For a long trade, your stop is the highest high of the last N periods minus (3 × ATR). As the stock rallies and reaches new highs, the highest high value increases, which means your stop moves higher. Your stop chases price upward. If price pulls back sharply, the stop is triggered and you're out with a profit.
Example: You buy a stock at 100p. The highest high over the last 5 periods is 105p. ATR is 2p. Your Chandelier stop is 105p - (3 × 2p) = 99p. As price rallies to 110p and the highest high becomes 110p, your stop moves up to 110p - 6p = 104p. Your stop is constantly rising as the trend develops. This is ideal for capturing trending moves while protecting gains.
For short trades: The logic reverses. Your stop is the lowest low of the last N periods plus (3 × ATR). As price drops and reaches new lows, the lowest low decreases, and your stop moves lower (giving more room on the downside).
The Chandelier Exit is powerful because it lets you ride strong trends without being whipsawed by small pullbacks. It's not a stop you place and forget—it updates dynamically. Most trading platforms can build this automatically, or you can manually update it daily.
This technique works best in strong trending markets. In ranging or choppy markets, the stop might get hit frequently. Use it when you have high conviction in a directional move.
Standard 14-Period Setting vs Alternatives
The default 14-period ATR is excellent for daily charts on most stocks. But like all indicators, you can adjust the period based on your timeframe and style.
Shorter periods (7 or 10 days): More responsive to recent volatility changes. Useful if you want tighter, faster-moving stops. Good for day traders or short-term swing traders.
Standard (14 periods): Balances responsiveness with stability. Works well for daily charts and typical swing trading timeframes. This is the standard for a reason—it's robust.
Longer periods (20 or 21 days): Smoother, less responsive to single days of volatility. Useful for position traders or those holding positions for weeks. The longer period gives a truer picture of ongoing volatility trends without daily noise.
Intraday (5 or 10 minutes): On 4-hour or 1-hour charts, you might use a 12-period ATR. On 15-minute charts, a 10-period ATR. The shorter the timeframe, the shorter the ATR period, because you're covering less absolute time.
Don't get hung up on finding the "perfect" period. Test a few (10, 14, 20) on your preferred timeframe and use whichever feels most natural. Consistency matters more than perfection.
ATR Applied to UK Stocks: Examples
FTSE 100 - Shell (SHEL): A large-cap with typically 0.5-1.5% daily ATR (varies with commodity prices). When you see ATR expand to 2%, volatility is elevated. Position sizing would be adjusted down.
FTSE 100 - Unilever (ULVR): A defensive blue chip with low ATR, typically 0.3-0.8% daily. When ATR is this low, moves are small. A pullback of 2% is normal and not a signal to exit. Your stops should be set wider (relative to the stock's range).
FTSE 250 - Barclays (BARC): A cyclical financials stock with higher ATR, typically 1.5-3% daily. When ATR compresses to 1%, you know a breakout is coming. Position sizing would increase because you're expecting a big move.
FTSE 250 - Rolls-Royce (RR): A volatile aerospace stock with ATR often 3-5% or higher. This stock moves a lot. Your stops should be wider, and position sizes smaller, to account for the volatility. A 2x ATR stop might be 8-10% away from entry—that's acceptable given the stock's nature.
The lesson: every stock is different. ATR lets you normalize these differences and trade each one appropriately. You don't apply the same stop distance to Shell and Rolls-Royce—you use ATR to adapt to each stock's characteristics.
Common Mistakes and Best Practices
Mistake 1: Using ATR without context. Don't just place 2x ATR stops mechanically. If a stock is in a strong uptrend and your 2x ATR stop would be below key support, consider using the support level instead. ATR is a guide, not a rule.
Mistake 2: Ignoring ATR changes. If ATR expands significantly on the day you enter a trade, your stop distance should expand too. If it contracts significantly, tighten your stops. Dynamic adjustment based on changing volatility is the whole point.
Mistake 3: Using ATR on illiquid stocks. ATR on low-volume stocks can spike on a single large trade. The indicator becomes unreliable. Use ATR on liquid stocks (FTSE 100, most FTSE 250) where volume is consistent.
Mistake 4: Confusing ATR with a direction signal. ATR measures volatility, not direction. High ATR doesn't mean the stock will go up; it means the stock will move more. Don't trade purely on ATR expansion. Combine it with other signals.
Mistake 5: Over-complicating position sizing. Simple is better. Pick a fixed percentage per trade (2% of account) and use ATR to determine position size. Adjust for high ATR days by trading smaller. Adjust for low ATR days by trading normal or slightly larger. That's enough sophistication.
Putting It All Together
ATR is a practical tool that solves real trading problems. It tells you how much a stock normally moves, so you can set appropriate stops. It helps you size positions consistently. It identifies breakout potential. And it powers trailing stop strategies like the Chandelier Exit.
The best traders obsess over risk management, not entry signals. ATR is a risk management tool. Master it, and you've solved one of trading's hardest problems: how to stay in winning trades and exit losing ones before they hurt too much. That's the path to consistent, long-term profitability.