Self Assessment/Student Loan Repayments

Hi everyone,

Just looking to get some advice from you all. In my current job I earn a salary of £18,330 per year, with occasional bonuses and small amounts of commission on top. This past summer I decided to take on some transcription work for an online company to supplement my income, which I'm still doing. The amount I earn varies from month to month, but it's a fairly small amount and I don't think the earnings will exceed £1,000 in any given tax year.

Part of the deal when signing up with this company is that I had to register as a sole trader. I've done this, have received a UTR, and appreciate that I will have to fill out a self-assessment for this income. As I use up my personal tax allowance in my main job, each month I put 20% of my self-employed earnings aside for tax. However, a change of circumstances has got me wondering about student loan repayments.

I'm signed up for Plan 2 SL repayments. Because my £18.3k salary is under the repayment threshold, I don't have anything deducted on my payslip, and because my self-employed earnings won't take me over £21k, I haven't been putting anything aside from these either.

However, next month will be starting a new job on a salary of £22,000, which obviously means there'll be Plan 2 deductions on my payslip each month. I also plan to put aside 9% of my self-employment earnings from now on. My question is, when I file my self-assessment next year, will HMRC tell me I have to pay 9% on ALL self-employment earnings in this tax year? Or is there any way for me to mark my earnings from August-October (where I was earning £18.3k) as exempt from this 9%?

Sorry for the long post, guys. It's my first time doing anything like this so any insight you can offer would be massively appreciated!