Stake splitting and rounding
How to split one total stake so every outcome returns the same, and what rounding and a book's maximum change.
The point of a surebet is that every outcome returns the same amount. That only happens if the total stake is split in the right proportions.
The formula
For a total stake T and decimal odds o₁, o₂, …, with S = 1/o₁ + 1/o₂ + …:
Stake on leg i = T × (1/oᵢ) / S
Every leg then returns T / S, which is above T when S is below 1.
Rounding
Round stakes are quicker to type, and some books only take whole amounts. Rounding moves the returns apart a little, so one outcome returns slightly more than the other. On small margins, heavy rounding (to 10 or 50) can eat most of it. Round to the smallest unit you're comfortable with and check the worst case.
When a book won't take your stake
If one book caps your stake (a maximum bet, or a limit on your account), the whole surebet scales down to it: the other legs must shrink in proportion, or they'd be uncovered. Work out the capped leg first, then the rest.
On our board
The stakes panel of every surebet does all of this for you: set your total stake, pick a rounding, set a maximum for a book, and it shows each leg's exact stake and what comes back either way. See Placing a surebet.
No account? The free surebet calculator does the same maths for 2 or 3 outcomes.
See it on real data
A free account shows up to 3 live surebets, each 0.99% or less, every leg re-checked at its book. No card needed.