The sole trader tax estimation tool applies the National Insurance rates to your business’ taxable profit, providing a breakdown per NI band.
We have assumed that all users are liable to pay both Class 2 and Class 4 National Insurance. These can be changed in your settings, where you can mark yourself as exempt from Class 4 National Insurance or state that you want to voluntarily pay Class 2 National Insurance even if you do not make enough taxable profit to be liable for it.