This paper explores the consequences of the timing of payments for the demand for money. It is found that if payments are the minimum of the money in the bank account or bills due, the demand for money will respond slowly to changes in income. This prediction disagrees with some formulations of the short-run demand for money (e.g., Irving Fisher's) but agrees with empirical estimates. The demand for money is adjusted to supply by changes in quantities (i.e., payments flows) rather than by changes in prices or interest rates.