Ten losing trades in a row at 1% of the account each leaves you down 9.6%, not 10%, because each loss is taken on a smaller balance than the one before. The same ten at 2% each leaves you down 18.3%. That single choice, made before the first entry, does more to your account than the entry price of any trade in the sequence.
Why position sizing decides the outcome
The entry price is an estimate. The size is arithmetic you control exactly.
Swing traders carry a risk day traders do not: the position is open while the market is shut. A stop is an instruction to trade once a price is touched, so an overnight gap through your level fills at the reopening price rather than at the stop. Size is the only part of that sequence you set in advance.
The arithmetic of drawdowns
Recovery is not symmetrical with the loss, because the gain has to be earned on the reduced balance.
- Lose 10%, and 11.1% on what remains gets you back to even (1 divided by 0.90).
- Lose 25%, and you need 33.3% (1 divided by 0.75).
- Lose 50%, and you need 100% (1 divided by 0.50).
The curve steepens the further down it goes, which is the whole argument for a size that keeps you on the shallow part of it.
Growth against preservation
Every trader has a loss size that changes their behaviour: the number that keeps them awake or pushes them into the next trade early. Sizing below that number is a decision about your own execution, not about the market.
The arithmetic of the choice is plain. At 1% risk per trade, the ten-loss sequence above costs 9.6%. At 2%, it costs 18.3%, and the recovery needed roughly doubles with it. Faster growth per winning trade is paid for with a deeper hole per losing streak.
The 1% rule and risk per trade
Fixed fractional sizing means risking a set percentage of current equity on each trade. One percent is a common choice, and it is a choice, not a law.
Risk in R terms
One unit of risk is called 1R. On a $50,000 account risking 1%, 1R is $500. That is the loss if the stop fills at your level.
Calculate 1R from current equity rather than the starting balance. At $60,000, 1R becomes $600; at $40,000, it becomes $400. The size shrinks as the account shrinks, which is what makes the drawdown curve above flatten instead of steepen.
Adjusting for volatility
Wider daily ranges push a structure-based stop further from the entry. That is arithmetic rather than a judgement call: the same dollar risk divided by a larger stop distance buys fewer shares.
If you also want a smaller dollar risk in fast conditions, set the trigger and the reduction in advance and write both down. A reduction decided while a position is moving against you is a discretionary trade wearing a rule's clothing.
Calculating position size
The formula is one line:
Shares = (Account equity x Risk %) / (Entry price - Stop price)
Step 1: set the stop from the chart
The stop belongs where the idea is wrong. That is a level on the chart: a support level, a moving average you are trading against, or a multiple of the Average True Range.
ATR is the average of the true range over a lookback. Each bar's true range is the largest of three distances: its high minus its low, its high to the previous close, and its low to the previous close. If a stock's ATR is $2.00, a $0.50 stop sits inside a single ordinary day's movement.
Step 2: divide
A worked example, with hypothetical figures:
- Account equity: $50,000.
- Risk per trade: 1%, so $500.
- Entry price: $150.00.
- Stop price: $142.00, at a support level.
- Risk per share: $8.00.
$500 divided by $8.00 is 62.5, so you buy 62 shares. Rounding down matters: 62 shares at $8.00 risks $496, while 63 would risk $504 and break the rule you just set.
Check the second number before you order. Those 62 shares cost $9,300, which is 18.6% of a $50,000 account in one position. A 1% risk and a large slice of capital are compatible when the stop is tight, and that concentration is a separate decision from the risk.
Total exposure and overnight risk
Risk per trade and total exposure are different numbers. Portfolio heat is what every open position loses together if all the stops fill. For each position, take the distance from entry to stop and multiply by the units still open. Convert to your portfolio currency, add them up, and divide by portfolio value.
Five positions at 1% each is 5% heat. Ten at 2% each is 20%, which is the number that matters when a single event moves everything at once.
Correlated positions
Four large technology names bought on four separate setups are not four independent risks. When they share the same customers, the same input costs and the same index membership, one sector-wide shock moves all four, and your 4% of separate risks behaves like a single 4% position.
Decide a cap for one sector's share of your open risk and apply it as a rule at entry, before the fifth idea in the same sector looks compelling.
Gaps
A stop does not cap the loss on a gap. If the close is $150 and the reopening print is $130, a stop at $142 fills near $130, and the loss is 2.5 times the planned 1R. Sizing is what keeps that outcome survivable, and it is the only defence available while the market is shut.
Scaling and dynamic sizing
Adding to a winning position
Pyramiding adds shares as a position moves your way. The claim to be careful about is the one that says this adds no risk.
Take the example above: 62 shares, entry $150, stop $142, $496 at risk. The price reaches $158 and you move the stop to $150, your entry. The original 62 shares now risk nothing. Adding 30 shares at $158 against that same $150 stop puts $240 of new risk on, so the position risks $240 rather than zero.
That can be the right trade. It is not a free one, and the arithmetic has to be done at the moment you add.
Sizing off your equity curve
Some traders reduce size during a drawdown and restore it when the curve recovers. The mechanical version of that is already built into fixed fractional sizing, because 1R falls with the balance.
An extra discretionary cut on top is a second bet: that your recent results predict your next ones. Decide whether you believe that before you build a rule on it.
Five sizing mistakes
- Increasing size after a loss to recover it in one trade, which raises the risk exactly when the balance is smaller.
- Size creep, drifting from 1% to 3% without deciding to.
- Ignoring liquidity, taking a position you cannot exit in a thin stock without moving the price against yourself.
- Round numbers, buying 100 shares because it is a round number rather than the 62 the arithmetic gives.
- Counting only per-trade risk, and missing that ten positions at 2% each is 20% of the account on the line at once.
Put a number on your own exposure
Swingfolio does this arithmetic on the screens where you make the decision.
The position size calculator takes your entry price, stop price, account value and risk percentage. It returns the share count, the investment amount, the risk amount and the stop distance as a percentage. Add a target price and it also returns the potential reward and the risk-reward ratio.
Inside the trade form, the risk preview updates as you type: expected risk, expected reward, the R:R ratio and the portfolio risk this trade represents. Above 5% of portfolio value, it prints a warning that the risk exceeds 5%.
On the dashboard, a Portfolio Heat gauge reads out your total open risk as a percentage. Below 6% it is labelled "Risk Under Control", from 6% "Elevated Risk", and from 10% "Excessive Risk!". Those thresholds are the app's own, and they are on screen so you can argue with them.
Open your last ten trades and calculate the dollar risk on each: entry minus stop, times units. If those ten numbers are not close to each other, sizing is the first thing to fix. Start the 30-day trial and let the form do the division.