Riches to rags every month?

"This paper finds declining consumption expenditure between paydays, for a typical household in the working population of the UK. The magnitude is inconsistent with exponential time preference, but compatible with quasi-hyperbolic discounting. However, the hyperbolic model predicts that credit constraints drive the decline, and we find only mixed evidence in this regard. We also observe a method-of-payment result that suggests a role for mental accounting: households choose declining cash spending but flat credit-card spending over the pay period. We propose an alternative explanation for the results, based on cognitive costs of budgeting and perceptual biases, rather than self-control problems"--Forschungsinstitut zur Zukunft der Arbeit web site.