The St. Patrick's Day parade in New York is usually held on March 17, but when it falls on Sunday, like this year, it is held on Saturday "due to religious observances," explained the New York City parade's official website. And this shift lends itself to an even better turnout for the restaurants and pubs as crowds stroll the streets after the parade on Saturday and continue celebrating through Sunday.
(Read More: How to Win Your March Madness Pool)
Not all cities have that restriction—Boston's parade will be held on Sunday, March 17—and some cities towns the U.S. have held their St. Patrick's Day's parade as early as the first weekend of March.
"We don't have any special discounts for this day. We feel like this is the day when we actually make money," said Ronaghen. His pub usually has lines outside from 11 a.m. to 3 p.m. during St. Patrick's Day celebrations.
On the national level, more than 133 million people will celebrate St. Patrick's Day this year, according to a National Retail Federation survey that polled 5,185 consumers in February.
(Read More: Maybe March Madness Is GOOD for Productivity)
On average, a celebrant will spend $35.27 on items such as something green to wear, festive corned beef and cabbage, as well as not forgetting to top it off with Irish whiskey or Guinness. In total the spending over this holiday is expected to rise to $4.7 billion, up from last year's $4.14 billion.
In Newark, N.J., for example, the party starts early—the city's St. Patrick's Day parade is scheduled for Friday afternoon. McGovern's Tavern in Newark expects to have an intense celebration through the whole weekend and will call its entire staff in.
"We'll be very busy all three days," said bar attender Mo McGovern, "All hands on deck."
Sean Muldoon, a founder of The Dead Rabbit Grocery and Grog, a two level Irish Pub in New York's financial district, wants to make sure that that the party stays strong on St. Patrick's Day itself.
"On Sunday, we'll have Irish music, Irish tap dancing and for the happy hour we offer a complementary beef stew," Muldoon said, explaining that for Saturday he does not offer any discounts.
(Read More: Buzzed: Drinking at the Vatican and the Ultimate Beer Internship)
All Irish establishments will have, most likely, the best weekend in the year, but even non-Irish related businesses will benefit from the St. Patrick's Day tradition of celebrating out.
For Courgette, a new American cuisine restaurant in Manhattan, New York, Irish celebration brings 20 percent more customers when held on the weekend, said manager Charlie Fernandez.
"This is the fourth best holiday for us," said Fernandez. Mothers' Day brings the most traffic, followed by Valentine's Day and the Christmas season, he continued.
To compete with Irish bars on St. Patrick's Day, Courgette gives a free shot of Jameson to everyone who walks in on Saturday. It is hard to change the food menu for just one day, Fernandez said, but Irish drinks are easier to accommodate. The restaurant is going to make green beer on site, by adding green food dye to light beers, like Bud Light or Corona Light—there is no St. Patrick's Day celebration without the traditional drinks.
All Irish whiskey sales peak around St. Patrick's Day and the sales tend to surpass all other spirits in March, said Hanna O'Leary, a Jameson brand ambassador, who works on promoting Jameson brand. She said that St. Patrick's day is the climax in sales for whiskey.
"We nicknamed it a second Christmas," said O'Leary.