You can use the calculators provided on HMRC’s website or other payroll software, to be able to calculate the tax and NI due in respect of your employees.
The tax which is due for a particular employee is calculated by reference to their gross pay with a deduction for their tax-free allowance. The tax-free allowance would reflect their circumstances (using their coding notice and the pay date). The remainder of the pay is subject to tax and this is calculated using the Basic PAYE tools or other software.
Tax is generally calculated on a cumulative basis, looking at the individual’s circumstances for the tax year to date.