An employee may have a non-standard tax code for a number of reasons. Some of the more common are that they have a second job, have another income from a pension or something like rental income. They may have benefits from your job that they need to pay tax on, for example a company car, or expenses from work that they need to pay tax on.
An employee’s code may also be changed if they have tax due from previous years from wages or pension.
Another reason may be that a new employee is put on a temporary emergency tax code when starting a new job
Further information about tax codes, national insurance and other PAYE topics can be found on the Gov.Org ‘s website here: