The different due to the auditor test calculated tax by see overall for salary of employee, that employee wasn't deduct taxable.
For Company, there is the calculation method which the revenue employee was excess of 20,000 baht, the company will bring in excess of 20,000 to calculate and deduct tax.
Sometime, the Company will round-up according to the company's opinion or if the employee who wishes to provide the tax increase, the employee will inform the purpose with to HR.
If the company has withheld exceeds the employee will make a tax refund from the Revenue Department.