I don't think it is necessary to have a joint accout before

marriage (it may complicate things) You guys can figure out approximatly what the total cost of mortgage (or rent), utilities, etc., and food would cost, and you can divide the expenses equitably -- it doesn't have to exactly 50-50, but if your incomes are comparable, your contributions should be comparable as well. Some people go by percentages of their salaries in dividing up househould contribution.