Average True Range (ATR) Calculator — Measure Volatility for Stop Losses

The Average True Range (ATR) is one of the most versatile and widely used volatility indicators in technical analysis. Developed by J. Welles Wilder Jr. in his 1978 book "New Concepts in Technical Trading Systems," ATR measures the average magnitude of daily price swings for an asset over a specified period. Unlike a simple range calculation that only considers the current day's high and low, ATR incorporates gaps between sessions by using the previous close in its calculation, giving a more complete and honest picture of actual volatility.

The genius of ATR lies in its simplicity and adaptability. It works for any asset class — stocks, forex, commodities, crypto, indices — and on any timeframe. It automatically adjusts to changing market conditions: expanding during volatile periods and contracting during calm ones. This adaptive quality makes ATR particularly valuable for stop-loss placement, because it ensures your stop distance reflects current market conditions rather than an arbitrary fixed percentage that might be too tight in volatile markets and too wide in quiet ones.

ATR is expressed in the same units as the price of the asset — dollars for stocks, pips for forex, points for indices. A stock trading at $200 with an ATR of $5 typically moves about $5 per day (including gaps). This absolute value is what makes ATR so practical for position sizing and stop-loss calculation: you can directly translate the ATR value into dollar risk per share, which feeds directly into your position sizing formula.

This ATR calculator takes three price inputs — high, low, and close — along with the previous session's close and a lookback period to compute the Average True Range.

High, Low, Close (Current Period)

Enter the highest price, lowest price, and closing price for the current trading period (typically a day). These three values define the trading range for the period. The high and low capture the full extent of price movement, while the close represents where the market settled.

Previous Close

Enter the closing price of the previous trading period. This is essential for the True Range calculation because it allows ATR to capture gaps. If the current high is higher than the previous close, the gap between the previous close and the current high is part of the true range. Without this value, gaps would be invisible to the volatility calculation.

ATR Period

Enter the number of periods to average. The standard default is 14 periods. A 14-period ATR on a daily chart averages the true ranges of the last 14 trading days. Shorter periods make ATR more responsive to recent volatility changes; longer periods produce a smoother, more stable reading. For day trading, 7 to 14 periods is common; for swing trading, 14 to 20; for position trading, 20 to 50.

The True Range formula is: True Range = Max(High − Low, |High − Previous Close|, |Low − Previous Close|).

This takes the largest of three values. The first (High − Low) is the simple intraday range. The second and third capture gaps by measuring the absolute distance from the previous close to the current high or low. If there is no gap, the simple range dominates and the True Range equals High − Low. If there is a gap up, the second value (|High − Previous Close|) dominates. If there is a gap down, the third value (|Low − Previous Close|) dominates.

The ATR is then calculated as a smoothed average of True Ranges. Wilder's original method uses an exponential smoothing: ATR_today = ((ATR_yesterday × (n − 1)) + True Range_today) / n, where n is the ATR period. For the first ATR calculation, a simple average of the first n True Ranges is used. This smoothing gives more weight to recent True Ranges while maintaining stability, making the ATR responsive to changing conditions without being overly reactive to single-session spikes.

Using a concrete example: if yesterday's ATR (14-period) was $4.50, today's True Range is $6.00, and the period is 14, today's ATR = ((4.50 × 13) + 6.00) / 14 = (58.50 + 6.00) / 14 = $4.61. The ATR increased slightly because today's range was larger than the average, pulling the smoothed average upward. If today's range had been $3.00 (below average), the ATR would have decreased.

Example 1: Setting a Stop Loss

A trader buys a stock at $150 with a 14-day ATR of $4.50. Using a 2x ATR stop loss, the stop is placed at $150 − (2 × $4.50) = $141. This means the trader is giving the stock room equal to twice its average daily swing. If the stock drops to $141, the trade is closed for a loss of $9 per share. The 2x ATR multiple is a common default — it is wide enough to survive most normal fluctuations but tight enough to limit losses if the trade goes wrong.

Example 2: Position Sizing

A trader with a $25,000 account wants to risk 1% per trade ($250). The stock has an ATR of $3.75, and the trader uses a 2x ATR stop ($7.50 per share). Position size: $250 / $7.50 = 33 shares. Total position value: 33 × entry price. If the stock is $100, the position is $3,300 — about 13% of the account. If the ATR were $7.50 instead, the position size would be $250 / $15 = 16 shares, or about 6.4% of the account. The higher volatility produces a smaller position, keeping dollar risk constant.

Example 3: Trailing Stop

A trader buys a stock at $80 with an ATR of $2.50. The initial 2x ATR trailing stop is at $75. The stock rallies to $95 over several weeks, and the trailing stop moves up to $95 − $5 = $90. The stock then pulls back to $91 — the stop is not triggered. The stock resumes its rally to $100, and the stop moves to $95. If the stock then drops below $95, the position is closed with a $15 gain per share. The trailing ATR stop automatically adapted to the stock's price level and maintained a consistent risk distance throughout the trade.

Choose the Right ATR Multiple for Your Style

The ATR multiple determines how wide your stop is. A 1.5x ATR stop is aggressive — it will be triggered more often by normal noise but will produce smaller losses when triggered. A 3x ATR stop is conservative — it gives the trade more room but risks larger losses. Day traders often use 1.5x to 2x ATR; swing traders use 2x to 3x ATR; position traders may use 3x to 5x ATR. The right multiple depends on your timeframe, the asset's typical volatility, and your risk tolerance. Start with 2x ATR and adjust based on your hit rate — if you are being stopped out too often, increase the multiple.

ATR Is Absolute, Not Percentage

A $5 ATR on a $50 stock (10%) is very different from a $5 ATR on a $500 stock (1%). Always convert ATR to a percentage of the current price when comparing volatility across assets of different price levels. ATR in absolute terms is useful for position sizing and stop placement on a single asset; percentage conversion is necessary for cross-asset comparison.

ATR Lags During Rapid Volatility Changes

ATR is a smoothed average, which means it lags behind sudden volatility spikes. During a flash crash or news-driven gap, ATR will not immediately reflect the full extent of the volatility expansion. If you are trading during extreme events, consider using a shorter ATR period or manually adjusting your stops to account for the current conditions rather than relying solely on the smoothed ATR reading.

Combine with Other Indicators

ATR alone does not tell you the direction of the trend — it only measures volatility. Combine ATR with trend indicators (moving averages, trendlines), momentum indicators (RSI, MACD), and support/resistance levels to form a complete trading plan. ATR-based stops work best when placed on the correct side of the trend: below support for long trades, above resistance for short trades, with the ATR multiple ensuring adequate room for normal fluctuations.

All content on this page is educational and does not constitute financial advice. ATR is a historical volatility measure and does not predict future price movements. For personalized guidance, consult a certified financial planner.