Want to be rich and skinny? Stop eating out.

The No. 1 thing Americans bust their budget on is dining out, according to research released Tuesday by financial company Principal. More than 1 in 4 Americans (26%) said that this was 2017’s top budget buster for them, followed closely by food/groceries (21%) and travel (20%).

One problem: People who eat out a lot tend to underestimate what this will cost them, according to a study released in March from researchers at Penn State. The researchers asked the participants what they thought they would spend eating out at the beginning of a two-week period and then in the middle of that period; participants upped their average budget from a little under $18 in week one to about $55 in week two.

Jay Zehngebot for Moneyish

“What this tells us is that obviously they thought they would spend less in a week, but as the week progressed they realized they were spending a lot more and they rationalized that increase,” says Amit Sharma, associate professor of hospitality management and director of the Food Decisions Research Laboratory, Penn State.

Not only is eating out wreaking havoc on your savings, it’s expanding your waistline. On days when Americans eat out, they scarf an average of 200 more calories than when they eat at home, according to a study of more than 12,500 people published by Public Health Nutrition in 2015. Furthermore, government research reveals that “when eating out, people either eat more or eat higher calorie foods — or both — and that this tendency appears to be increasing” and additional studies have found that dining out is associated with obesity and more body fat.

This story was originally published in March and has been updated.