DaveJB said:
Hehehe, remember we let them build a wall to stop the sassenachs treading on the heather
The only 'personal' thing about position sizing is knowing how much cash you are prepared to blow if things get really bad (emergency stop).
Say you had £10,000 (obviously petty cash to you, Dave)
You decide that you are prepared to place a maximum of £2500 per position and were prepared to loses a maximum of £250 against your '****, get me outta here' position - as opposed to a more gentlemanly scramble for the door if things just don't look right. So, you are prepared to hold 25% of total capital in any one position and prepared to risk 2.5% at any one time.
For arguments sake consider the following targeted trade:
Trading at 105 having just broken a double bottom at 100 from 70, giving you a target of 130. You note the major support at 85 and a reaction low at 80.
Your initial plan for the trade is to buy at 105 with a controlled exit if the price closes below 85 and an emergency exit at 79. Target 130.
The maths:
The total travel you are prepared to put up with is 105-79=29 points. The maximum cash you are prepared to lose is £250, less dealing costs (for arguments sake £15). So the maximum amount of shares you can buy against your maximum pain is (250-15)/0.29 = 810 shares.
Buying 810 shares at the current price would cost £850.5 - well within your maximum of £2500 per position.
Your targeted exit is 130 so your profit should it be hit is 25 per share - £202.5 - less the pleasure - £187.50.
As this stands some may take the deal, others not as the risk/reward ratio is less than 1:1 - you are risking £250 to make £187.50 - again we are back to personal choice.
As the trade progresses - assuming it goes up! The stops can be moved accordingly - say the price gets to 115, some may decide to lift the initial stop to 100 and the emergency stop to 90. If you are wanting to live with purely % stops, then just alter the figures accordingly.
That just saved you the cost of a book
Of course Mr Van Tharp is famous for his position sizing, which is why he gave all his pension money to one guy - who then defrauded him of the lot. (allegedly/apparently etc...)