In the lottery, players select numbers that they hope will be randomly selected in a drawing. If no one picks all six winning numbers, the jackpot rolls over to the next drawing, and so on. The jackpot can grow to extraordinary amounts, incentivizing more and more people to buy tickets. But how much is it actually possible to win? We asked a math professor to calculate the odds.

In addition to the prize money awarded to a winner of a jackpot, many lotteries allow winners to choose between receiving a lump sum payout or an annuity paid out over a set number of years (and with applicable taxes). The new Powerball jackpot is $1.2 billion with a cash option of $516 million for Wednesday night’s drawing. The majority of winners choose the annuity, which will pay out annual payments for 30 years.

It’s not surprising that so few people win jackpots: A person’s chance of winning a major prize is about one in 300 million, which is equivalent to flipping heads on a coin 28 times in a row. However, there are a few small things that can tip those odds in your favor.

Lottery games need mega-sized jackpots to drive ticket sales and attract attention on news sites and TV broadcasts. The way to make sure those jackpots get bigger on a regular basis is to make the game harder to win. That’s exactly what organizers of the Powerball and Mega Millions have done for decades, Victor Matheson, an economics professor at the College of the Holy Cross, explains to NerdWallet.