Yeah... Excel is the quick and dirty way to do this... In the simplest form, you want to have 5 columns... and 2 "fixed" cells:
Columns: BetNumber, BetAmount, SumWagered, WinAmount, Profit
Fixed Cells: Multiplier, Payout
First Row formulas:
BetNumber=1
BetAmount=0.00000001
SumWagered=BetAmount
WinAmount=BetAmount*Payout
Profit=WinAmount-SumWagered
2nd (and further rows):
BetNumber=PreviousBetNumber+1
BetAmount=PreviousBetAmount*Multiplier
SumWagered=PreviousSumWagered+BetAmount
WinAmount=BetAmount*Payout
Profit=WinAmount-SumWagered
To determine the "max" number of rounds you can survive... I plug in a "guess" for the first BetAmount value... then look down to the row where SumWagered > Balance... the BetNumber BEFORE that row is the max number of losses before you can no longer wager. Make first BetAmount smaller to make max Rounds bigger... and vice versa
I'm not sure of an easier way to explain it
I could upload a basic spreadsheet somewhere if you let me know what format you need...