If you are self employed then you will generally be expected to pay Class 4 National Insurance.  The amount you pay is based on a percentage of your self employment profits, between a certain threshold.

How Much is Class 4 National Insurance?

For 2017/2018 Class 4 National Insurance is:

9% on profits between £8,164 and £45,000

2% on profits over £45,000

How Do you Pay Class 4 National Insurance?

If you are self employed, need to submit a Self Assessment Tax Return by 31 January each year which details your trading income for the previous tax year, as well as how much income tax your need to pay.  You need to include the amount of Class 4 National Insurance you need to pay on this return too.

Is There Anything Else I May Need to Pay?

Yes, you may need to pay Class 2 National Insurance.