An apparatus for estimating blood pressure, the apparatus comprising: a sensor configured to measure (410, 510) a bio-signal from an object; and a processor configured to: obtain (420, 520) a cardiac output, CO, feature based on the bio-signal; obtain (450, 550) a total peripheral resistance, TPR, feature by combining an amplitude of a propagation wave component and amplitudes of at least two reflection wave components of the bio-signal, in response to a variation of the CO feature at a blood pressure measurement time relative to a calibration time being above a predetermined lower CO-limit and below a predetermined upper CO-limit; obtain (460, 570) the TPR feature by combining the amplitude of the propagation wave component and an amplitude of one reflection wave component of the at least two reflection wave components, in response to the variation of the CO feature being located below the predetermined lower CO-limit or located above the predetermined upper CO-limit; and estimate (470, 580) blood pressure based on the CO feature and the TPR feature, wherein the processor is further configured, in response to a variation of the CO feature being above a predetermined lower CO-limit and below a predetermined upper CO-limit, to: linearly combine an amplitude of a first reflection wave component and an amplitude of a second reflection wave component, among the at least two reflection wave components, to obtain a combination result; and obtain a ratio between the combination result and the amplitude of the propagation wave component as the TPR feature, and wherein the processor is further configured to obtain, as the TPR feature, a ratio between the amplitude of the one reflection wave component and the amplitude of the propagation wave component, in response to the variation of the CO feature being located below the predetermined lower CO-limit or located above the predetermined upper CO-limit. a sensor configured to measure (410, 510) a bio-signal from an object; and a processor configured to: obtain (420, 520) a cardiac output, CO, feature based on the bio-signal; obtain (450, 550) a total peripheral resistance, TPR, feature by combining an amplitude of a propagation wave component and amplitudes of at least two reflection wave components of the bio-signal, in response to a variation of the CO feature at a blood pressure measurement time relative to a calibration time being above a predetermined lower CO-limit and below a predetermined upper CO-limit; obtain (460, 570) the TPR feature by combining the amplitude of the propagation wave component and an amplitude of one reflection wave component of the at least two reflection wave components, in response to the variation of the CO feature being located below the predetermined lower CO-limit or located above the predetermined upper CO-limit; and estimate (470, 580) blood pressure based on the CO feature and the TPR feature, obtain (420, 520) a cardiac output, CO, feature based on the bio-signal; obtain (450, 550) a total peripheral resistance, TPR, feature by combining an amplitude of a propagation wave component and amplitudes of at least two reflection wave components of the bio-signal, in response to a variation of the CO feature at a blood pressure measurement time relative to a calibration time being above a predetermined lower CO-limit and below a predetermined upper CO-limit; obtain (460, 570) the TPR feature by combining the amplitude of the propagation wave component and an amplitude of one reflection wave component of the at least two reflection wave components, in response to the variation of the CO feature being located below the predetermined lower CO-limit or located above the predetermined upper CO-limit; and estimate (470, 580) blood pressure based on the CO feature and the TPR feature, wherein the processor is further configured, in response to a variation of the CO feature being above a predetermined lower CO-limit and below a predetermined upper CO-limit, to: linearly combine an amplitude of a first reflection wave component and an amplitude of a second reflection wave component, among the at least two reflection wave components, to obtain a combination result; and obtain a ratio between the combination result and the amplitude of the propagation wave component as the TPR feature, and linearly combine an amplitude of a first reflection wave component and an amplitude of a second reflection wave component, among the at least two reflection wave components, to obtain a combination result; and obtain a ratio between the combination result and the amplitude of the propagation wave component as the TPR feature, and wherein the processor is further configured to obtain, as the TPR feature, a ratio between the amplitude of the one reflection wave component and the amplitude of the propagation wave component, in response to the variation of the CO feature being located below the predetermined lower CO-limit or located above the predetermined upper CO-limit.