Over 80% of adjacent quarters contain a different number of business days due to fluctuations in the number of public holidays and weekend days. We first provide evidence that business days have different associations with revenues and earnings compared to holidays and weekends. We also show that analysts’ forecasts are strongly associated with the results in the adjacent quarter. Together, these results indicate it is important to adjust for quarter length when making revenue and earnings forecasts. We examine whether analysts appear to make appropriate adjustments for the quarterly change in business days, which can be determined easily via a calendar. We find the change in business days is positively associated with analysts’ revenue and earnings forecasts error, which indicates analysts systematically underestimate (overestimate) performance when quarter length increases (decreases). We then examine whether managers strategically adjust their voluntary disclosures. We find managers are more (less) likely to explicitly mention the length of the quarter during conference calls when the quarter is shorter (longer) than the preceding quarter, consistent with managers taking credit for good performance driven by longer quarters and blaming poor performance on shorter quarters. We also find firms are more (less) likely to issue management forecasts when the change in business days is negative (positive). In summary, our evidence suggests analysts fail to fully take account of the quasimechanical effect that quarter length has on performance and managers strategically alter their voluntary disclosures to take advantage of these failures.