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Risk and position sizing

ATR Position Size Calculator

A fixed stop is too tight in a volatile market and too wide in a quiet one. Enter the ATR and let the stop adapt while the risk stays the same.

Your risk

Volatility

In price units, on the timeframe you trade.
1.5 to 2 is common. Below 1 the stop sits inside ordinary noise.
Units for forex, multiplier for futures, 1 for shares and crypto.
Position size—
Stop distance—
Money at risk—
Risk per unit of size—
Stop as a multiple of ATR1.5× ATR

Sizing from ATR keeps the money at risk constant while the stop distance adapts to conditions — wider in volatile markets, tighter in quiet ones. The position size moves inversely, which is the point: the same rule produces a smaller position exactly when the market is capable of larger moves.

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How it works

stop distance = ATR × multiple
position size = (balance × risk%) ÷ (stop distance × value per price unit)

The money at risk is fixed by your rule. The stop distance comes from the instrument's own recent movement. The size is whatever makes those two agree — which means it falls automatically when volatility rises.

That last property is the point. A fixed 20-pip stop is generous in a quiet session and inside the noise during a news week; an ATR-based stop is the same distance relative to how the instrument is actually moving.

Choosing the multiple

Multiple Behaviour
Under 1× Inside ordinary movement — hit by noise
1.5× Common for intraday; outside most single-bar moves
2× Standard for swing entries
3×+ Trend following, where being stopped out early is the main risk

Below 1× ATR the stop is inside the range the instrument covers in a normal period, so it gets triggered by movement rather than by the idea failing. That shows up as a poor win rate on trades that were directionally right — a stop-placement problem that looks like a strategy problem, and the two get treated very differently.

The field other ATR calculators skip

Most assume one asset class. This one asks for the value of one price unit per contract, which is what makes the same arithmetic work everywhere:

  • Forex: the units in the position — 100,000 for a standard lot.
  • Futures: the contract multiplier — 50 for ES, 5 for MES.
  • Shares and spot crypto: 1, since one unit of price is one currency unit per share or coin.

Without that field the tool silently belongs to whichever market its author had in mind, and produces a confidently wrong size everywhere else.

What ATR does not do

It is backward-looking. ATR describes the last N periods. Volatility regimes change faster than the average does, and it lags most at exactly the moments that matter — the first day of a new regime is sized on the old one.

It ignores structure. A level does not care about the average range. When the ATR stop and the obvious invalidation level disagree, the level is the one carrying information; ATR is a sanity check on distance, not a substitute for a reason.

It says nothing about correlation. Three positions each sized correctly by ATR can still be one bet — see the correlation calculator.

FAQ

What ATR multiple should I use for a stop?

1.5× to 2× covers most intraday and swing approaches. Below 1× the stop sits inside normal movement; above 3× it is trend-following territory where early stop-outs are the greater risk.

Which ATR period should I use?

14 is the standard and a reasonable default. Shorter periods react faster and produce noisier sizing; longer ones are more stable and slower to notice a change in conditions.

Is ATR sizing better than a fixed stop?

It adapts, which is usually an improvement — the same rule produces a wider stop and a smaller position when the market is capable of larger moves. It is not better when a structural level gives a clearer invalidation point.

Does ATR work on all instruments?

The arithmetic does, provided the value of one price unit is entered correctly. That figure differs by asset class and is the input most often got wrong when moving between markets.

Should the position size change every day as ATR changes?

For a new position, yes — that is the mechanism working. Recalculating an open position's size mid-trade is a different decision and usually a worse one, since it means adding or trimming for reasons unrelated to the trade.

This is the plan. What did you actually do?

A calculator tells you the size you should have taken. It cannot tell you the size you took at 2pm after two losers, or how often your stop moved once price went against you. Drop in a statement from MT4/MT5, a broker CSV or a crypto export and see the answer for your own last 90 trades.

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