EATER –  In 2014 Tennessee pastor Chad Roberts started a website for frustrated restaurant workers to vent about Sunday diners. The website, called Sundays Are The Worst, was his response to an incident the year before in which a different pastor tried to avoid an automatic gratuity fee at Applebee’s, writing on her receipt “I give God 10 percent, why should you get 18.” Since then, the Sunday morning dining crowd (churchgoers) has gotten a reputation of being bad tippers. This prompted Roberts to start a dialogue and let servers know, as he writes on the site, that “not all Christians are like this.”

Turns out, Roberts might be right. Data shows that while Sundays may be one of the worst days for restaurant workers to make tips, it’s not because Sunday diners are bad tippers. In fact, Sunday customers are actually the most generous tippers, at least at some restaurants.

On average, diners actually tip more on Sunday mornings during brunch and lunch service, compared to every other day of the week, according to exclusive data from point of sale and restaurant management technology company CAKE. While the average American tip at independent restaurants is, according to the data, 16 percent on any given day, Sunday mornings between 10 a.m. and 12 p.m. see an average tip of 20 percent.

CAKE’s data comes from credit card transactions from about 2,000 independent quick service and full service restaurants nationwide. The company compared total revenue to total tips to find the average percentage of tips the restaurants’ servers make every hour between 10 a.m. and 11 p.m. But the differences CAKE sees might only apply to certain types of restaurants, said Mike Lynn, a consumer behavior professor at Cornell University, specializing in tipping research. “This difference could simply be the make up the kinds of restaurants people are going to,” he said. The types of restaurants people visit on Sundays and the weekends might be completely different than the kinds of restaurants people visit during the week. “There’s huge variability in quick service and full service,” Lynn said. For example, a family may have a larger dinner at a full service restaurant on Sunday, but eat fast food during the week.

While Sunday morning is the best time for finding generous tippers, late evenings on any day except Monday make a close second. Discounting Monday nights, evenings at 10 p.m. yield some of the highest tips, the data show: People tip at CAKE restaurants at 18 percent percent during the evenings after 6 p.m. and at 19 percent at 10 p.m., when tipping seems to peak, nightly.

The worst tippers? Diners on every morning besides Sunday. Breakfast times, before noon, yield an average of 13 to 14 percent tips, according to CAKE data. Then there are Monday nights. People give some of the lowest tips on the first night of the work week, an average of 16 percent after 6 p.m. and numbering 12 percent at 10 p.m., the hour when restaurants usually see the largest tips of the day.

But the tip percentage only tells part of the story, Mani Kulasooriya, CAKE CEO, said in an email. The company compared average tips to total revenue, which points to different conclusions for restaurant owners. The comparison showed that while Sunday tips are higher than other days, restaurants make more revenue on other days, like Friday.

“So people are tipping more generously on Sundays, but servers still make the most on Fridays because overall revenue is higher on Friday than Sunday,” Kulasooriya said. For restaurant owners, this could mean adjusting shifts and rotations so that servers can maximize their tips and be happier employers.

Data analysis like this is part of a new trend in the restaurant industry in which restaurants collect tons of data on their customers and use it to direct business. Restaurant owners can use tip and revenue data, for instance, to rate performance, Kulasooriya said. ”If a server working on Sunday can get the same percentage as the one on Monday, we know that the Monday person is significantly outperforming the Sunday person,” he said. “We currently believe independent operators do not look at this, but should.“

The time of year also seems to have some affect on how people tip. Last year CAKE looked at holiday tipping and found that during the winter holiday season, tipping was down seven percent, compared to the rest of the year. But on the actual holidays (Thanksgiving, Christmas, and New Year’s Day), tipping was up three percent, compared to normal days throughout the year.

But as the data on tipping shows some patterns, understanding the reasons behind the patterns is a challenge, Lynn said. There are lots of variables that can influence tippers, the most obvious being the overall bill: the higher the bill, the higher the tip would be. Other factors like the server’s perceived attractiveness and service quality also come into play. But little research has been done on how days of the week or time of day psychologically influence tipping — and few researchers are looking into it, because it’s just not that interesting to them, Lynn said.

But the data could be particularly relevant at a time when tipping is a hot debate in the restaurant industry. Many restaurant owners are getting rid of tipping altogether and are simply paying servers better. As technology makes analyzing tipping practices more accessible, could more restaurant owners start reconsidering tipping’s place in their business models?