In MR heads, read-nonlinearity and write-nonlinearity, which is manifested in phenomena such as nonlinear transition shift (NLTS), degrade the bit error rate (BER) performance in a PRML read channel. We discuss a simple method of estimating these nonlinearity effects for a PRML read channel, and compare the calculated and experimental results. In a PRML read channel, the BER can be easily calculated from the noise deviation after the equalization, and the nonlinearities increase the noise deviation. The calculation and experimental results show a proportional relationship between the noise deviation due to read nonlinearity and the absolute value of the amplitude asymmetry. The deviation due to NLTS can be calculated by considering the first and second adjacent transition shifts and write precompensation. The total effects of the nonlinearities are easily calculated by adding the squares of all the noise deviations.