Help with formula for setting a maximum dollar value for order quantity

[tradingcat]

Hi, I've got a buy at market hotkey which helps me automatically work out position size based on how much I want to risk, ask price, and stop loss price. I have it set up as per image below (It's set to risk $30 per trade).

I'm now trying to incorporate a way to have a cap on the maximum position size, at say $10,000. How would I put that into the formula? Tried searching through help & forums on how to do this but couldn't figure it out.

 

Edited February 16, 2023 by tradingcat
typo

[Mike Medved]

When you say maximum position size, you mean you don't want to add more to existing position if it is $10K?

[tradingcat]

Sorry I wasn't very clear. I mean just for this one trade. So if I already have $15k of this position, I don't mind buying more. just that I want this specific trade capped at a specific amount.

[Mike Medved]

well.. you have Qty as 30/(Ask-PriceAtMouse). Should really be floor(30/(Ask-PriceAtMouse)) - because quantity is an integer.

So then the total amount of the transaction would be (since it is a Market Buy, let's assume it is at Ask)

Ask * floor(30/(Ask-PriceAtMouse))

You don't want that to be more than $10k, so that amount would be

Min(10000, Ask * floor(30/(Ask-PriceAtMouse)))

Thus the appropriate quantity should be that amount divided by Ask (and floor taken for it so that it is integer)

floor(Min(10000, Ask * floor(30/(Ask-PriceAtMouse))) / Ask)