A raffle odds calculator works out your real chance of taking something home. Five tickets in a raffle that sold 500, with three prizes drawn, gives you about a 3% chance of winning at least one. That’s 1 in 34. Buy 20 tickets and it’s about 11.5%. The free calculator above does the exact sum for any raffle, from a school tombola to a big charity draw, and it accounts for the fact that a ticket can only win once.
How the raffle odds calculator works
The neat way to get the answer is to work out the chance of winning nothing and take it away from 1. With N tickets sold, t of them yours and k prizes:
Chance of no prize = C(N − t, k) ÷ C(N, k) Chance of at least one = 1 − that
C(n, k) counts the ways to choose k tickets from n. So the top line counts every draw that misses all of your tickets, out of every possible draw. For one prize it simplifies to t ÷ N, which is what most people expect.
The calculator also shows expected prizes (t × k ÷ N) and, if you add a ticket price and prize value, the expected value of your tickets.
Is it worth buying more tickets?
More tickets always help, but each one helps a little less once there are several prizes, because two of your tickets can’t both win the same prize. And almost every raffle has a negative expected value, since the prizes are worth less than the money raised. That’s the point: the gap is what goes to the cause. Buy as many as you’re happy to give.
Running the raffle yourself? The raffle ticket generator makes numbered tickets and draws the winners, and the random name picker works for name-in-a-hat draws.
For Ireland’s Christmas raffle, the Millionaire Raffle odds calculator has the full prize list.