Hi James,
Glad to be of help.
In regards to your question on the additional funds and next position size, essentially, yes, I do as you have written. As the overall portfolio ‘value’ increases by the amount injected, say $1000 in your example, then assuming I had to fill all 10 positions, then it would be as you have stated.
Often however, I might only have 2 or 3 positions that may be ‘open’ or available to fill when the additional funds are injected, so it’s then a bit trickier to be perfectly precise with your position sizing.
e.g. let’s say I had 7 positions already filled at or close to my $1000 ‘previous’ position size.
As such, using your example $10,000 account, I should have close to $7000 (based on cost) ‘in the market’ already. If I then injected my $1000 extra, then to get all my available money into the market, my position size increases to $1333.33 per position. (being then $4K / 3 positions) instead of the $1,100 per position based on the overall account value (being now $11,000). If I only purchase stocks based on $1100 each, then I’ll still have $700 cash sitting idly doing nothing in my account. It might not sound like much, but that more than 6% of the $11,000 portfolio!
The other curveball to throw in however, is that sometimes (in fact, essentially every time) you will find yourself in a position where your position sizes vary based on the growth (or declines) or individual positions already in the market. You might have a stock that’s already grown by 50% to $1500 from the original position, and others that might be say $700.
At these times, I then aim to take the philosophy of again trying to have all my money in the market working for me, and so essentially I take the open cash available (including any funds that were available prior to the injection), and divide this by the number of open positions available. What you will find is that sometimes you might start the new positions slightly ‘higher’ than 10% (assuming 10 positions in the portfolio) after the cash injection, but it won’t be materially higher, and I think outweighs having cash sitting idly about not working for you.
Beyond Charts does a good job of doing all of this automatically (so was all that a waste of time?
), and also factoring in a percentage of open profit, which is probably a great way to start, but just some things to keep in mind.
Hope this helps!
Best,
Graeme