A small delay is normal. Based on clinical data, blood glucose measured with a fingerstick (BGM) is typically about 3–5 minutes ahead of glucose measured in interstitial fluid by a CGM. (1) Lag time may be greater when glucose is changing rapidly, such as after eating or during exercise.
Reference:
1. Alva S, et al. Accuracy of a 14-Day Factory-Calibrated Continuous Glucose Monitoring System With Advanced Algorithm in Pediatric and Adult Population With Diabetes. J Diabetes Sci Technol. 2022 Jan;16(1):70-77. https://pubmed.ncbi.nlm.nih.gov/32954812/