There is no separate second-job tax rate. Your second income stacks on top of your main income and is taxed at whatever band it falls into. Because your £12,570 personal allowance is normally used by your main job, even a small second income is usually taxed from 20% up.
For self-employed side income, the first £1,000 can be covered by the trading allowance instead of expenses, and Class 4 National Insurance applies to the profit above that. This calculator shows the tax and what you keep.
If your self-employed side income grows past the Making Tax Digital threshold, you will need to keep digital records and file quarterly.
Your personal allowance is usually used up by your main job, so your second income is taxed from the basic rate upward — and can tip into the higher-rate band.
The first £1,000 of self-employed or side income each year can be tax-free. Above that you report it; you claim either the allowance or your actual expenses, whichever is larger.
Self-employed side income counts towards the MTD threshold once your combined gross income passes the limit for your phase.
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