We compared the glucose management indicator (GMI) calculated using 14 days of continuous glucose monitor (CGM) data with GMI calculated using <14 days. Analysis included 581 individuals with type 1 diabetes or type 2 diabetes from five clinical trials. The correlation between the 14- and 7-day GMI was 0.95 and the correlation between 14 days versus 10, 5, and 3 days GMI was 0.98, 0.91, and 0.86, respectively. The percentages of GMI values within 0.3% of the 14-day GMI were 98% with 10-day GMI, 87% with 7-day GMI, 77% with 5-day GMI, and 60% with 3-day GMI. Minimal differences were observed between GMI computed using 14 days of data compared with GMI computed with 7 days. Although 10-14 days of CGM data are preferred for computing GMI, for most patients a satisfactory estimate of HbA1c can be obtained with 7 days of data.