Assume you have 100k. How much would you allocate to one day trade position on average? 10k? 20k? 100k? 200k?
You need to define the instrument being traded. Big difference between 100k on cash T-bonds and 100k day trade margin on T-bond futures.
Position sizing depends on volatility, volume and confidence. One symbol I track regularly I would use all 100K without concern. The volatility is low, the volume supports that amount, and I'm confident in my system. Conversely, consider shorting Best Buy last week based on negative news reports. The volatility is higher because news reports are less predictable than other technical or fundamental triggers; the volume would make it tough to get more than 50K in quickly; and using news reports as a trigger lessen my confidence in the trade. So in the 2nd example I would have used 50K instead of 100K. Last of all, it depends on experience. Until someone can trade 10K at a time with a high percentage of successful trades they shouldn't go to 25K. Once they can do 25K, then move to 50K, etc. Most traders don't follow this system, and that has a lot to do with why the failure rate is > 90% in this business.
I will go up as high as 5% of account size per trade for whatever position I am trading at the time......my max.
If you're name is barney frank, you'd evidently be willing to put $700 billion on one position. Oh, I'm sorry, that was with our money, not his. My bad.
You have to do a Risk-Reward analysis. If the Risk is high, engage a lower %. Also, your confidence level in the position. Like the old saying says... If the odds are overwhelmingly in your favor, BET THE HOUSE!
When you arn't 100% sure your profitable then use very small amounts like 1-10%. When you are 100% sure you are profitable the only thing your doing money managment wise is refraining from risky leverage positions. At least that is always in the back of my mind. Leverage is like cigarrettes even if you've never done it before.