Sizing against a stop that moves: the problem ATR bands create
The band that makes this system adaptive also makes the stop distance a moving target. Sizing has to account for that, or per-trade risk quietly triples in exactly the conditions that produce the largest losses.
Key takeaway
- Stop distance here is a function of current volatility, so the position size must be recalculated at every entry — not set once
- A volatility spike widens the channel, which means a smaller position, not a wider risk
- The middle-line stop can sit 3 ATR away on entry; sizing for 2 ATR and using it is a silent 50% risk increase
The stop distance is not a constant
In a system with a fixed percentage stop, the distance is known in advance and sizing is one calculation you can do once. Here it is not: the channel width is a function of current ATR, and ATR in a given market can easily double between a quiet month and a volatile one.
If the stop distance doubles and the position size does not halve, the risk on that trade has doubled — and it has doubled precisely in the conditions most likely to produce a large adverse move.
This is the failure that turns a well-behaved system into an account-ending one, and it is entirely silent. Nothing on the chart looks different. The position size is the same number of contracts it always was, and the loss when it comes is twice what the backtest suggested.
Risk first, then distance, then size
- Fix the risk per trade as a fraction of the account. Half a percent to one percent is a sensible range for a swing system taking a few trades a week.
- Measure the stop distance for this entry — the current gap to the middle line, or your fixed ATR multiple, in the instrument's own units.
- Divide. Position size is the dollar risk divided by the dollar value of that distance. Do this at every entry, not once per market.
Done this way the volatility of the market has been divided out. A wide channel produces a small position and a narrow one a large position, and both lose the same amount if the stop is hit — which is the only condition under which a run of losses is survivable.
The middle-line stop needs measuring, not assuming
The middle-line stop is attractive because it trails. What is easy to miss is how far away it is at the moment of entry: you entered on a close beyond the upper band, which by construction is two ATR above the EMA. Your stop is therefore at least two ATR away, and if price ran further beyond the band, more.
A swing system's risk is about frequency, not just size
Holding periods here run days to weeks, so a portfolio of these positions turns over far faster than a Turtle-style position system. More trades means more opportunities for a correlated cluster to open at once.
- Cap the total open risk, not just the per-trade risk. Six percent at risk across all open positions is a conventional ceiling.
- Watch correlated entries. A volatility expansion tends to hit a whole sector at once, and this system signals on volatility expansion.
- Count costs honestly. At a few trades a week, spread and commission are a real subtraction from expectancy, not a rounding error.
Common questions
- Should ATR for sizing be the same ATR as the bands?
- It is simplest if it is, and it keeps the two parts of the system consistent. If you use a different lookback for sizing than for the bands, be clear about why — otherwise you have two volatility estimates disagreeing, and the disagreement will be largest in fast markets.
- What if the channel is so wide the position size rounds to zero?
- Then the correct action is not to trade that market today. A position size below one unit is the sizing rule telling you the market's current volatility is too large for your account to take this trade at your stated risk. Overriding it is the same as raising your risk without saying so.
The ideas behind it
This system assumes you already know these. Each one is explained from scratch in Investing 101.
These are documented methods described for study. Nothing here is investment advice, a recommendation, or a claim about future returns — every system on this page has losing periods, and the pages say where.
Reading about a system is not having one.
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