How to calculate the stake required to win $\$X$ at $Y$ odds I want to cover a $\$100$ bet I have on the Hawthorn Hawks winning the Australian Football League grand final. If they lose the grand final, I lose my $\$100$. Another team, Geelong Cats, are at $\$4.25$ to win the grand final. How do I calculate the stake required at odds of $4.25$ to win a $100$ dollar profit from the bet (which might cover my Hawks bet if Geelong win). i.e. If I put $31$ dollars on at $4.25$, I would receive $131.75$ if I won my bet. Take away my $31$ dollar stake, and I am left with $\$100.75$. I want to know the equation to calculate what exact stake I need to make a profit of $\$100$. Note: I'm a hobby gambler.

$$4.25 x = x+100\\\ 3.25x = 100 \\\ x=\frac{100}{3.25} = 30.769 $$ If you bet \$30.77 you come away with \$130.77; the bookie keeps the odd quarter penny.