All the standard NI rates for United Kingdom and Isle of Man are already built into the system. Although there is provision for users to change them, it is recommended that they are left alone. If any of the rates change, we will email all registered users informing them of what the changes are and how much the upgrade will cost.
The NI rates are used in the NI calculation where an amount of NI is dependant on a level of NI Liable pay.
Consult the HMRC's NI calculation specifications if you wish to know how each parameter affects the NI calculation.