Hello, if you have any questions or need further clarification after reading my answer please let me know.
Karolina, thank you for your question...
A) Is my 2nd job employed or self employed? I work for a translation and interpretation
agency on an ad-hoc basis who pay fixed rates for each job.
You could argue this is self employment and not employment. This being the case you should register for self assessment as self employed. You can register online and the link is here
Look for Register online for self assessment and national insurance contributions
B) I pay tax and NI in my main employment. How much Tax and NI will I have to pay for
my 2nd self employed job?
As far as tax is concerned, provided your total income from all sources is below £41,450 in the current tax year before personal allowance of £9,440, you will pay tax at basic rate of 20%.
For NI contributions, you will only have to pay Class 2 NI if your earnings from self employment are in excess of £5,725 per year (2013-14) and the NI rate is £2.70 per week.
C) How and when do I pay this? Do I need to do a self assessment?
You will pay tax and Class 4 NI once you have filed your tax return as the tax/Class 4 NI is calculated when you file your self assessment tax return. Normally tax is payable in two instalments – Jan and Jul. For tax year 2013-14 the payment dates are Jan 2013 and Jul 2013. Any balance outstanding must be cleared before Jan 2014.
More information on Class 2 National Insurance is covered here
If you need more information please let me know before you rate my service.
I hope this is helpful and answers your question. If you are happy and there are no more issues I will appreciate if you would kindly rate the service I provided to ensure I get paid for it.
I am available for any follow up questions you may have, and you can use the reply button to post your follow up questions to the page.