Supporting Guidance: employer compliance: guidance by subject: inaccuracies: employee’s tax code not known
To compute the tax due when an employer has not made deductions from payments to an employee who did not
- produce form P45,
- complete the Real Time Information (RTI) starter checklist (or equivalent) or
- sign form P46
- calculate the tax due in accordance with the online tool available on gov.uk - Work out your new employee’s tax code.