AbstractNear-infrared spectroscopy (NiRS) is a relatively new technology of brain imaging with its potential in the assessment of cerebrovascular health only recently discovered. Encouraging early results suggest that NiRS can be used as an inexpensive and portable cerebrovascular health tracking device using a recently proposed pulse relaxation function (PReFx). In this paper, we propose a new NiRS timing index, $\text {TI}_{\rm NiRS}$ TI NiRS , of cerebrovascular health. $\text {TI}_{\rm NiRS}$ TI NiRS is a novel use of the NiRS technology. $\text {TI}_{\rm NiRS}$ TI NiRS is motivated by the previously proved relationship of the timing of the reflected wave with vascular resistance and compliance in the context of pressure waveforms. We correlated both $\text {TI}_{\rm NiRS}$ TI NiRS and PReFx against age, a non-exercise cardiorespiratory fitness (CRF) index, and two existing indices of cerebrovascular health, namely transcranial Doppler (TCD) augmentation index, $\text {AI}_{\rm TCD}$ AI TCD , and magnetic resonance imaging (MRI) blood flow pulsatility index, $\text {PI}_{\rm MRI}$ PI MRI . The $\text {TI}_{\rm NiRS}$ TI NiRS correlations with Age, CRF, $\text {PI}_{\rm MRI}$ PI MRI and $\text {AI}_{\rm TCD}$ AI TCD all are significant, i.e., $r=0.53$ r = 0.53 ($p=0.002$ p = 0.002 ), $r=-0.44$ r = - 0.44 ($p=0.011$ p = 0.011 ), $r=0.45$ r = 0.45 ($p=0.012$ p = 0.012 ) and $r=0.46$ r = 0.46 ($p=0.010$ p = 0.010 ), respectively. PReFx, however, did not have significant correlations with any of the vascular health factors. The proposed timing index is a reliable indicator of cerebrovascular aging factors in the NiRS waveform.