Mega Millions jackpot: How odds of winning are slimmer than ever

Update: Mega Millions jackpot nears record level

The Mega Millions jackpot is on track to shatter the record for a U.S. lottery. If no one gets the right numbers by Christmas Eve, the number could soar to $1 billion.

But for now, players are only thinking about Tuesday night's drawing.

With a jackpot well over half a billion dollars, 75 million tickets have already been sold. Mega Millions lottery officials expect to sell another $170 million more Tuesday, making the odds of winning slimmer than ever.

In New York City, Helen Tirado, felt like making a bet. She said, "I only bought four, just thinking: 'You know what? They say, 'All you need is a dollar to win.' We are four people on it so we're hoping for the best."

Unfortunately for Tirado and others like her, changes in recent months mean dwindled chances for winning Mega Millions. Odds of winning the jackpot used to be 1 in 176 million. This past October, those odds changed to 1 in 259 million. Players used to have to pick six numbers from 1 to 56, but now it's 1 to 75. 

Since Mega Millions changed the rules, there has not been a winner, and that drives up the jackpot. 

Tuesday's prize is already the fourth largest in U.S. history. Over the last 20 months, Mega Millions and Powerball -- its main competitor -- have had five jackpots more than $400 million.

1. $656M, Mega Millions, March 30, 2012

2. $590.5M, Powerball, May 18, 2013

3. $587.5M, Powerball, Nov. 28, 2012

4. $586M, Mega Millions -- current jackpot

5. $448.4M, Powerball, Aug. 7, 2013

Sociology professor Iddo Tavory studies the behavior of how people make decisions. He says when lottery players start to fantasize about their future after winning the lottery, their choice to enter seems rational.

"What houses they would buy, what they would buy their mother, what they would buy their friends, what car they would drive," Tavory said. "Where you feel like there's actually something there that could happen, not just kind of a fantasy you're having out of nowhere, I mean then, the odds don't matter that much."

Lottery officials tell CBS News, the majority of Mega Millions sales come on the final day -- and with today's snow across parts of the country -- we will have to wait to see how that affects the projected $250 million in sales.