Vast heart rate (HR) data during daily activities are being accumulated with widespread use of wearable sensors. To interpret the meaning of these HR data, the reference point of HR in individual subject is required. Although resting HR has been used for this purpose, the definition of resting HR has not been established and particularly, the effects of time of the day (circadian rhythm) on resting HR have not been considered. One of the other candidates for the reference point may be basal HR, i.e., the lowest HR in the day. In the present study, we therefore investigated the characteristics of basal HR by examining the effects of age and sex on basal HR and the occurrence time of basal HR during 24 h in 113,341 males and 140,332 females extracted from a 24-h Holter ECG database of the Allostatic State Mapping by Ambulatory ECG Repository (ALLSTAR). Although basal HR decreases with age until 20 yr old in both sexes, it increases slightly with advancing age thereafter. Although the clock time to reach basal HR appears between 02 and 05 h on average, it shows progress or delay depending on the time of life. The difference between 24-h mean and basal HR decrease linearly with age, suggesting that age-dependent decline in the increases in HR with daily activities can be detected by using basal HR as the reference point.