VOLATILITY GUIDE · ATR AND POSITION SIZE
ATR position sizing: volatility-based stops and trade size
1. Understand what ATR measures—and what it does not
ATR measures the magnitude of recent price movement. A rising ATR indicates wider bars or gaps; it does not distinguish bullish from bearish movement. Values are in the instrument's price units, so an ATR of 30 index points cannot be compared directly with an ATR of $1.20 in another market without converting each to money or a percentage.
- ATR is volatility, not trend direction or target probability.
- The same numeric ATR means different monetary risk for products with different point values.
- ATR depends on bar timeframe, lookback length, session data and smoothing implementation.
- A sudden volatility shock enters the average after it occurs; ATR does not forecast the gap that causes it.
2. Calculate True Range and ATR
TR = max(high − low, |high − previous close|, |low − previous close|)ATRₜ = (previous ATR × (n − 1) + current TR) ÷ nA 14-period setting is common, but '14' has no meaning without the bar interval: 14 one-minute bars and 14 daily bars describe very different horizons. Platforms can initialize or smooth ATR differently and may include different trading sessions, so verify the displayed value rather than assuming two charts are identical.
| High | Low | Previous close | Largest component | TR |
|---|---|---|---|---|
| 105 | 99 | 101 | high − low | 6 |
| 108 | 104 | 102 | high − previous close | 6 |
| 103 | 98 | 106 | previous close − low | 8 |
3. Match timeframe, lookback and multiplier to the strategy
The ATR input should represent the volatility horizon that can invalidate the setup. An intraday trade may use intraday bars; a multi-day position may use daily bars. A shorter lookback reacts faster but changes size more abruptly, while a longer lookback is smoother but slower to reflect a regime shift.
| Parameter | Lower value | Higher value |
|---|---|---|
| Lookback | More responsive, noisier | Smoother, slower |
| ATR multiplier | Tighter stop, larger size | Wider stop, smaller size |
| Bar timeframe | Short-horizon movement | Longer-horizon movement |
4. Turn ATR into a defensible stop distance
One method places the stop k × ATR from entry. Another starts from a structural invalidation level and uses ATR as a noise buffer or minimum-distance check. The second preserves the market thesis; the first is easier to standardize. Neither makes the stop an execution guarantee.
stop distance = ATR × chosen multiplierstop distance = max(distance to structural invalidation, ATR × minimum multiplier)For a long trade, subtract the validated distance from entry; for a short trade, add it. Then align the stop to the instrument's tick or price increment in the conservative direction and recalculate the exact distance after rounding.
5. Convert ATR distance into position size
unit risk = (ATR stop distance + adverse slippage) × monetary value per point + round-turn feesquantity = floor(effective risk budget ÷ unit risk, to the allowed size increment)For shares, value per point is normally the currency value per one-price-unit move for one share. For futures, use the contract point or tick value. For CFD and forex lots, use the broker-specific monetary value for the chosen symbol and account currency. Conversion errors can overwhelm the benefit of volatility adjustment.
6. Worked futures example: MNQ with a 1.5 ATR stop
| Input | Value | Meaning |
|---|---|---|
| Effective budget | $250 | Smallest available risk ceiling |
| ATR | 28 points | Value from the selected chart settings |
| Multiplier | 1.5 | 42-point stop distance |
| MNQ point value | $2 | $84 gross loss per contract |
| Slippage + fees | $3.20 | $87.20 total unit risk |
floor($250 ÷ $87.20) = 2 MNQ; planned total risk = $174.40If ATR rises to 42 points with the same 1.5 multiplier, distance becomes 63 points and unit risk is approximately $129.20 with the same costs. The budget then supports only one MNQ. Volatility-adjusted sizing reduces quantity as recent movement expands.
7. Worked generic CFD example and broker conversion
Assume an index CFD shows ATR = 12 points, the validated multiplier is 2, and one full lot is worth $1 per point in the account currency. A 24-point stop risks $24 per lot before costs. With $1.50 estimated spread, slippage and commissions per lot, unit risk is $25.50.
$100 budget ÷ $25.50 = 3.921 lots; at a 0.01 lot step, size = 3.92 lots8. Control regime changes and portfolio risk
ATR equalizes a chosen amount of planned stop risk, not every kind of risk. Several positions sized from their own ATR can still share a common factor and gap together. A low ATR after quiet trading can also produce a large quantity immediately before volatility expands.
- Cap quantity, notional exposure, margin use and total open risk separately.
- Stress a volatility jump and a gap larger than the ATR stop.
- Group correlated positions instead of treating each ATR budget independently.
- Define when ATR is sampled so size does not change unpredictably during order preparation.
- Recalculate after tick rounding, currency conversion and broker size limits.
9. Limitations and implementation checklist
- ATR is backward-looking and does not predict direction or future volatility.
- Results differ with timeframe, session, lookback, data feed and smoothing method.
- A volatility stop can conflict with structural invalidation if applied mechanically.
- Very low ATR can create excessive quantity unless separate caps exist.
- Stops can fill beyond their trigger; stop-limit orders can remain unfilled.
- Fees, spread, slippage, tick alignment and account-currency conversion belong in unit risk.
- Validate the full strategy out of sample and monitor realized R, not only the indicator settings.
Questions about ATR position sizing
What ATR period should I use for position sizing?
There is no universal period. The bar timeframe and lookback must match the strategy's holding horizon and be validated with the complete entry/exit process. Fourteen periods is common, not mandatory.
Is 1.5 ATR or 2 ATR a better stop?
Neither multiplier is inherently better. A tighter multiple raises size and stop frequency; a wider one lowers size and changes the trade. Test the entire method after costs and against structural invalidation.
Does ATR position sizing keep risk constant?
It can keep estimated stop risk near a chosen budget by changing quantity. It cannot keep realized loss constant because gaps, slippage, changing volatility and correlated positions remain.
Can ATR compare volatility across instruments?
Raw ATR cannot be compared directly across differently priced products. Convert it to percentage terms or monetary movement using each product's point value and currency conversion.
When should ATR be recalculated?
Define a consistent sampling point, such as the completed bar used by the strategy. Recalculating from an unfinished bar while preparing an order can make the stop and quantity unstable.
Primary sources and verification date
Risk parameters, market conditions and order behavior can change. Verify product specifications and broker rules before placing an order.
- Average True Range (ATR)Fidelity Learning Center
Defines True Range, recursive ATR, common periods, non-directionality and volatility-based stop use.
- Calculating Futures Contract Profit or LossCME Group
Connects ATR and typical price movement to tick value and monetary contract fluctuation.
- Position and Risk ManagementCME Group
Covers product volatility, contract count, stops and margin as separate risk variables.
- Stop Orders: Factors to Consider During Volatile MarketsFINRA
Documents stop execution uncertainty during fast markets and non-execution risk for stop-limit orders.