An apparatus for estimating bio-information, the apparatus comprising: a sensor (100, 830) configured to obtain a bio-signal from an object; and a processor configured to obtain a second-order differential signal of the bio-signal, to detect at least one of an inflection point in a predetermined period of the second-order differential signal, and a zero-crossing point in the predetermined period of the second-order differential signal, to extract a feature based on the detected at least one of the inflection point and the zero-crossing point, and to estimate bio-information based on the extracted feature, wherein the processor is further configured to, based on the inflection point not being detected in the predetermined period of the second-order differential signal, determine whether the zero-crossing point is present in the predetermined period of the second-order differential signal based on at least one predetermined criterion, and wherein the at least one predetermined criterion comprises at least one of: a first criterion as to whether a first value, obtained by subtracting a time corresponding to a first local maximum point of the second-order differential signal from a time corresponding to a first local minimum point of the second-order differential signal, is greater than a first threshold; or a second criterion as to whether the first value is greater than a value, obtained by multiplying a second value with a second threshold, the second value being obtained by subtracting the time corresponding to the first local minimum point from a time corresponding to a second local maximum point of the second-order differential signal. a sensor (100, 830) configured to obtain a bio-signal from an object; and a processor configured to obtain a second-order differential signal of the bio-signal, to detect at least one of an inflection point in a predetermined period of the second-order differential signal, and a zero-crossing point in the predetermined period of the second-order differential signal, to extract a feature based on the detected at least one of the inflection point and the zero-crossing point, and to estimate bio-information based on the extracted feature, wherein the processor is further configured to, based on the inflection point not being detected in the predetermined period of the second-order differential signal, determine whether the zero-crossing point is present in the predetermined period of the second-order differential signal based on at least one predetermined criterion, and wherein the at least one predetermined criterion comprises at least one of: a first criterion as to whether a first value, obtained by subtracting a time corresponding to a first local maximum point of the second-order differential signal from a time corresponding to a first local minimum point of the second-order differential signal, is greater than a first threshold; or a second criterion as to whether the first value is greater than a value, obtained by multiplying a second value with a second threshold, the second value being obtained by subtracting the time corresponding to the first local minimum point from a time corresponding to a second local maximum point of the second-order differential signal. a first criterion as to whether a first value, obtained by subtracting a time corresponding to a first local maximum point of the second-order differential signal from a time corresponding to a first local minimum point of the second-order differential signal, is greater than a first threshold; or a second criterion as to whether the first value is greater than a value, obtained by multiplying a second value with a second threshold, the second value being obtained by subtracting the time corresponding to the first local minimum point from a time corresponding to a second local maximum point of the second-order differential signal.