Methods and systems for estimating MRA for a hard disk drive are described. The methods and systems described herein provide for real time estimating and correcting magneto-resistive head asymmetry (MRA) in a hard disk drive using analog-to-digital convertor (ADC) samples or counts. Generally, ADC outputs may be obtained by injecting MRA at known values, where an estimated MRA may be derived in real time by applying an equation using particular ADC output values. Once an estimated MRA is obtained, MRA correction may be performed when the estimated MRA is larger than a threshold value, such as by adjusting a channel MRA compensation coefficient.