Position sizing without guessing
The one number that decides how long you last, the arithmetic behind it, and the two mistakes that quietly break it.
How many losing trades your limits survive
A percentage limit sounds abstract until you convert it into the number of ordinary stop-outs it allows. That number is the honest size of your runway.
In short
- Divide the dollar allowance behind each limit by your planned loss per trade to get the losses it survives.
- The daily limit usually binds early in an account; the remaining total drawdown takes over after a losing stretch.
- Sizing so that one stop-out cannot use a whole allowance is the difference between a bad day and a breach.
Percentages hide the runway
A firm that allows a 5 percent daily loss and a 10 percent maximum drawdown has told you something important, but not in the unit you experience. Nobody trades in percentages. You trade in positions, and positions end in wins or losses of roughly the size you planned. The honest reading of any limit is the count of ordinary losing trades it survives.
The conversion is one division. On a 100,000 dollar account, a 5 percent daily limit is a 5,000 dollar allowance. If your planned loss per trade is 1,000 dollars, the rule survives five ordinary stop-outs in a day. Five sounds different from 5 percent. It is the same rule, stated in trades instead of marketing.
Which limit actually binds
Early in an account the daily limit is usually the tighter one, because the total drawdown allowance is still untouched. After a losing week the picture flips: the remaining total shrinks with every loss you keep, while the daily allowance resets each morning. The ceiling on your size is always the smaller of the two allowances at that moment.
This is why the same trader can be comfortably sized on Monday and dangerously sized on Thursday without changing anything. The rules did not move. The room behind them did. Recomputing the count after a drawdown, using what is actually left, is the discipline that keeps an ordinary losing streak from becoming a terminal one.
Size so one loss cannot end the week
Working backward from the allowance gives a ceiling: the size at which a single stopped-out trade lands exactly on the tighter limit. Trading at that ceiling means one ordinary loss uses everything. Most funded traders sit far below it, so that a normal cluster of losses, which every strategy produces, stays a bad day rather than a breach.
The calculators on the tools page do this arithmetic live: the drawdown guard counts the losses each limit survives, and the max lots calculator names the binding limit for your exact numbers. Neither is advice. They are the division and the comparison, done honestly, before the market does them for you.
Recount after every losing day
The count is not a set-and-forget number. Every kept loss shrinks the total allowance, and every reset morning restores the daily one, so the runway you had at the start of the week is not the runway you have on Thursday. A thirty second recount after a losing day, using the remaining allowance rather than the brochure figure, keeps the size honest.
Traders who breach rarely do it on their worst trade. They do it on an ordinary trade taken at a size the account could afford last week. The count is how you notice that the week has changed before the rules notice it for you.
Where to go next
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