An electronic device comprising: an optical sensor configured to emit a reference light to a reference object and detect the reference light reflected from the reference object during calibration, and emit a measurement light to a target object and detect the measurement light reflected from the target object during a measurement; a display; and a processor configured to: when the electronic device is placed on a charger and is in a charging state, perform the calibration of the optical sensor based on the reference light reflected from the reference object; control the display to output guide information for estimating bio-information according to progress stages of the measurement after charging of the electronic device ; and estimate the bio-information based on a light quantity of the measurement light that is reflected from the target object, and a light quantity of the reference light reflected from the reference object, characterised in that the optical sensor comprises a light source disposed at a center of the optical sensor , and a plurality of detectors arranged to surround the light source , wherein the processor is further configured to determine a contact position of the target object based on absorbances measured by the plurality of detectors , and wherein in response to the target object coming into contact with the optical sensor , the processor is further configured to determine the contact position and guide a user to change or maintain the contact position based on the determination of the contact position. an optical sensor configured to emit a reference light to a reference object and detect the reference light reflected from the reference object during calibration, and emit a measurement light to a target object and detect the measurement light reflected from the target object during a measurement; a display; and a processor configured to: when the electronic device is placed on a charger and is in a charging state, perform the calibration of the optical sensor based on the reference light reflected from the reference object; control the display to output guide information for estimating bio-information according to progress stages of the measurement after charging of the electronic device ; and estimate the bio-information based on a light quantity of the measurement light that is reflected from the target object, and a light quantity of the reference light reflected from the reference object, when the electronic device is placed on a charger and is in a charging state, perform the calibration of the optical sensor based on the reference light reflected from the reference object; control the display to output guide information for estimating bio-information according to progress stages of the measurement after charging of the electronic device ; and estimate the bio-information based on a light quantity of the measurement light that is reflected from the target object, and a light quantity of the reference light reflected from the reference object, characterised in that the optical sensor comprises a light source disposed at a center of the optical sensor , and a plurality of detectors arranged to surround the light source , wherein the processor is further configured to determine a contact position of the target object based on absorbances measured by the plurality of detectors , and wherein in response to the target object coming into contact with the optical sensor , the processor is further configured to determine the contact position and guide a user to change or maintain the contact position based on the determination of the contact position. <EOS>