An apparatus for estimating blood pressure, the apparatus comprising: a bio-signal measurer configured to measure a bio-signal from a user; and a processor configured to: extract one or more feature values from the bio-signal, wherein the one or more feature values comprise a first feature value associated with cardiac output and a second feature value associated with total peripheral resistance, adjust a combination coefficient for combining the one or more feature values based on a reference value including a vascular compliance index, obtain a first variation in the first feature value compared to a first reference feature value, and a second variation in the second feature value compared to a second reference feature value, and obtain a third variation based on the first variation and the second variation, and estimate a blood pressure based on the adjusted combination coefficient and the first variation, the second variation, and the third variation, wherein the processor is further configured to obtain the reference value, the first reference feature value, and the second reference feature value at a reference time including at least one of a calibration time of the bio-signal and a time at which the user is in a stable state. a bio-signal measurer configured to measure a bio-signal from a user; and a processor configured to: extract one or more feature values from the bio-signal, wherein the one or more feature values comprise a first feature value associated with cardiac output and a second feature value associated with total peripheral resistance, adjust a combination coefficient for combining the one or more feature values based on a reference value including a vascular compliance index, obtain a first variation in the first feature value compared to a first reference feature value, and a second variation in the second feature value compared to a second reference feature value, and obtain a third variation based on the first variation and the second variation, and estimate a blood pressure based on the adjusted combination coefficient and the first variation, the second variation, and the third variation, wherein the processor is further configured to obtain the reference value, the first reference feature value, and the second reference feature value at a reference time including at least one of a calibration time of the bio-signal and a time at which the user is in a stable state. extract one or more feature values from the bio-signal, wherein the one or more feature values comprise a first feature value associated with cardiac output and a second feature value associated with total peripheral resistance, adjust a combination coefficient for combining the one or more feature values based on a reference value including a vascular compliance index, obtain a first variation in the first feature value compared to a first reference feature value, and a second variation in the second feature value compared to a second reference feature value, and obtain a third variation based on the first variation and the second variation, and estimate a blood pressure based on the adjusted combination coefficient and the first variation, the second variation, and the third variation, wherein the processor is further configured to obtain the reference value, the first reference feature value, and the second reference feature value at a reference time including at least one of a calibration time of the bio-signal and a time at which the user is in a stable state. <EOS>