partnership agreement percentage ownership

if you have three partners–for example, one who is in charge of finances, one who will head up the business dealings, and one who will manage marketing–with each partner pitching in $33,333, then an even split of ownership is probably a good place to start. you need both to start and maintain a functioning company, but you need to decide what fair compensation is for the amount of risk each person is taking. will each of these people be working the same long nights and putting in the same amount of effort from the get-go to get the company going? it’s a tough call, but this is the bit where partner disagreements often arise. will existing partners give up an equal number of shares, or will it be based on percentage?