when should maaser be taken

I have money coming in from one venture and would like to put it all directly into another venture. Do I need to pay maaser on the those funds or only on funds i allocate for my personal use?

Only funds you take out of your businesses for personal use. The money you leave in your business does not require maaser yet.

In therory this is a simple calculation: Each year you calculate all profits from all ventures combined and you give maaser on that number. This means if you lost $100 in venture A and profited $150 in venture B you would only give maaser on your net profit of $50.