Trade journaling · Intermediate

Using Journal Data To Refine Position Sizing

The two figures that should set your risk per trade are already in your journal, and neither is in the rule of thumb you started with.

Last reviewed 15 September 2026 by the MarketPro research desk · Editorial policy

In short

Pull two figures from your log: the longest run of consecutive losses you have actually had, and how much your results swing from trade to trade. Apply that streak to your current risk setting to see the drawdown it produces, then size for a streak several trades longer than your worst, because the observed maximum is a lower bound rather than a worst case. Read the risk column for drift while you are in there.

What to remember

Your longest recorded streak is a lower bound, not a worst case. Size against something several trades longer.
Recovery takes about the same 37 trades at 1%, 2% or 3%. What changes is the depth you have to sit in while it happens.
Read the risk column against trade number. A nominal 1% that ranges from 0.6% to 1.9% is not a setting.
No number is waiting in the data. The log tells you what a drawdown costs, not which one you can tolerate.

Lesson 13 of 14 in Trade journaling and review

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Two numbers your log already holds

Position size is usually decided once, early, and then left alone. Your journal holds the two figures that should actually set it: the longest losing streak you have genuinely experienced, and how much your results swing from trade to trade. Both are already recorded, and neither appears anywhere in the rule of thumb that handed you 1% or 2% in the first place.

The streak tells you how deep a hole your current risk setting digs. The variability tells you how often you should expect to be in one. Together they turn sizing from a preference into a measurement you can re-run every quarter.

Nine losses in a row at 1%, 2% and 3%

Say your longest recorded run is nine consecutive losses across 340 trades. Here is what that same run costs at three risk settings, with the gain needed to get back to level.

Risk per trade	After 9 losses	Gain needed	Trades at +0.25R to recover
1%	-8.6%	+9.4%	37
2%	-16.6%	+19.9%	37
3%	-24.0%	+31.6%	37

The percentages are the obvious part. The less obvious part is the final column: recovery takes the same 37 trades at all three settings, because the loss and the recovery both scale with the same risk figure. What changes is the depth you have to sit in while those 37 trades play out, and depth is what ends accounts, usually through abandonment rather than a margin call.

At 3% the account is down a quarter and 37 trades from level. Most people do not trade the same plan through that. They cut size at the worst moment, or stop, or start looking for a different method, and all three turn a recoverable stretch into a permanent one. The drawdown calculator lets you run your own streak length against your own risk figure.

Why your longest streak is not the longest you will see

Nine is what happened in 340 trades. That is a lower bound on what is possible, not a worst case. At a 45% win rate, runs of nine losses are common enough that a longer one is close to expected across the next few hundred trades, and your sample has simply not run long enough to show it yet.

So size for a streak longer than your worst. Adding four or five to the observed maximum is crude and defensible. The formal version of the same question, how likely a given risk setting is to take an account below a threshold before the edge asserts itself, is what the risk of ruin calculator answers, and the answers are usually more sobering than intuition expects.

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Sizing drift: the 0.8% that became 1.9%

Pull the risk column and read it against trade number. It should be a flat line. It almost never is.

After winners. Risk creeps up following a good run, so the largest positions sit exactly where a streak is most likely to start, at the top of the equity curve.
After losers. Risk shrinks following a drawdown, which puts the smallest positions on during the recovery and makes the recovery take longer than it should.
By setup. Favourite setups get sized larger with no written reason. Check whether the ones you size up actually carry the higher expectancy, because the correlation frequently runs the other way.

The combination is the damaging part. Sizing up into strength and down into weakness can turn a positive expectancy into a worse outcome than trading every position at one fixed size would have produced, and it happens without anybody deciding to do it. A fixed percentage, computed on the position size calculator before each entry, removes the entire class of problem.

What the journal will not decide for you

There is no correct number waiting in the data. The log can tell you what 2% did to your account in your worst recorded stretch, and whether your sizing has been consistent, but the choice between a 17% drawdown you can sit through and a 25% one you cannot is about you, not about arithmetic.

Two further limits are worth naming. The streaks in your log come from the market conditions you have actually traded, and a regime you have not met yet can produce worse. And size interacts with margin: holding risk at a fixed percentage means a tighter stop buys a larger position, so the same 1% risked behind a 20 pip stop puts roughly four times as much notional on as it does behind an 80 pip stop. A rule that sits comfortably inside your margin on swing trades can press against it on short-stop entries in the same account.

Re-running the number each quarter

Treat sizing as a quarterly decision with three inputs.

Longest streak to date, plus a margin. Recompute it every time, because it only ever grows.
The maximum drawdown you are prepared to trade through, stated as a number before you are in one.
Whether the risk column was flat last quarter. If it drifted, fix the drift before changing the level, because a nominal 1% that is really 0.6% to 1.9% is not a setting at all.

Write the resulting figure into the plan with the date and the reasoning beside it. A year later, when a good run makes 2% feel conservative, the note explaining why 1% was chosen in the middle of a drawdown is the most useful sentence in the document.

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Work it through on your own position size. Nothing leaves your browser and there is no sign-up: Drawdown calculator, Risk of ruin calculator.

Written and reviewed by the MarketPro research desk

MarketPro is a trading-signal and trading-education app operated by Harajuku Holdings LTD (Cyprus). Our signal desk publishes and tracks every trade idea in-app, and every page here is checked against the app's live behaviour before publishing. Last reviewed 15 September 2026. How we produce signals and content · About MarketPro

FAQ

Using Journal Data To Refine Position Sizing: questions

How does a trading journal help with position sizing?

It supplies the inputs a rule of thumb cannot: the longest losing streak you have genuinely experienced, how much your results swing from trade to trade, and whether your risk per trade has drifted. Applying that streak to your current risk setting shows the drawdown it produces, which is a far more concrete basis for the decision than a generic 1% or 2%.

Should I reduce position size after a losing streak?

Cutting size inside a defined drawdown is a legitimate written rule, for example halving risk below 15% from the peak. What causes damage is unplanned drift, where size shrinks after losses and grows after wins with no decision being made, because that puts the largest positions at the top of the equity curve and the smallest ones during the recovery.

Is my longest recorded losing streak a worst case?

No, it is a lower bound. Nine consecutive losses in 340 trades means nine has happened, not that ten cannot. At a 45% win rate, a run of ten or more inside the next few hundred trades would be unremarkable, so sizing is normally done against a streak somewhat longer than the worst you have seen.

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