If function with changing parameters

I don't know if I titled this correctly.

My scenario (in words) is this: I have a profit amount per year. Investor A receives 100% of the profit until he is repaid his original investment. All of the profits after that are split 50/50 between investor A and investor B.

I have an IF function to determine, if the cumulative total is more than the amount of the original investment, then the cell yields 50% of the profit. If FALSE, the cell yields 100% of profit.

The problem is the target original investment is hit mid year. So I need a formula that says, pay 100% of profit cell until cumulative total hits original investment cell, then multiply the remainder by 50%. All in one formula.

Thanks in advance.

Try

=IF(CumProfit<=Investment),CumProfit,(Cumprofit-Invetsment)*0.5)