Most of the transformer have efficiency of 90-99%. This means the wastage of the power is negligible. The above analysis was for an ideal transformer. In a real transformer the energy losses are due to various reasons as detailed below.

1. Leakage of magnetic flux: Due to the air gaps in the core the amount of magnetic flux linked with the secondary is less than that of the primary as the energy is lost. It can be reduced by winding the primary and secondary coils over one another.

2. Iron loss: This is the energy lost as heat due to induced eddy currents in the iron core (alternating magnetic flux induces these currents). This loss is also called the eddy current loss. This is reduced by making core of laminated sheets of soft iron insulated from each other.

3. Copper loss: It is the heat energy lost across the resistance of copper windings used in primary and secondary coils. This loss can be minimised by using thick copper wire for the primary and secondary windings.

4. Hysteresis loss: This loss is due to heating up of core due to its repeated cycles of magnetisation and demagnetisation when an alternating emf is applied across the primary. This loss can be minimised by selecting a core material having a narrow hysteresis loop.

5. Magnetostriction: It is the loss due to the humming sound produced in the transformer.