Answer: Friday

If you weigh yourself every day, you’ll certainly notice fluctuations in your weight over time. Track those fluctuations long enough and you’ll likely notice a trend: you’re heavier at the start of the business week than you are at the end.

Researchers from the VTT Technical Research Centre of Finland, Cornell University, and Tampere University of Technology tracked the weight of 80 healthy adults over the course of a year. The study participants were the lightest on Friday and the heaviest on Monday. Weekend activities (dining with friends, alcohol consumption, more time to snack, etc.) contributed to small gains in weight and then, over the course of the week, busier schedules and more structured eating tended to whittle away at the retained weight until a low point on Friday.

Analysis of the participants’ behavior and weight loss also indicated that participants who were more aware of their weekend indulgences did a better job of restricting their dietary choices during the week to help balance out the fun they’d had (and intended to have again in the future).