An apparatus for estimating a concentration of an analyte may include a spectrum acquisition device configured to acquire a first in vivo spectrum of an object, and a processor configured to estimate the concentration of the analyte using the first in vivo spectrum and a concentration estimation model that is generated based on a second in vivo spectrum measured during a timeframe in which the concentration of the analyte in the object is substantially constant, and update the concentration estimation model based on the first in vivo spectrum and the estimated concentration of the analyte.