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.