Quick answer:
For your first Self Assessment, register as self-employed with HMRC by 5 October after the tax year you started trading, keep digital records of income and expenses from day one, note the 31 January deadline, and set aside money for tax as you earn. Software that tracks everything in real time makes the first year far less daunting.
Step 1: Register with HMRC
Once you start working for yourself, register for Self Assessment. The deadline is 5 October following the end of the tax year in which you began trading, for example, if you started in the 2025/26 tax year, you must register by 5 October 2026. Registering late can lead to penalties, so do it early.
Step 2: Keep records from day one
Start recording income and expenses immediately. The biggest first-year mistake is letting it pile up; clean digital records from the start make filing simple and your tax estimate accurate.
Step 3: Know your deadlines
- 31 January: file your online return and pay the tax you owe for the previous tax year, see GOV.UK Self Assessment deadlines.
- Payments on account: if your bill is over £1,000, you’ll usually make advance payments towards next year’s tax in two instalments (31 January and 31 July).
- If MTD for Income Tax applies to you, quarterly updates replace the once-a-year approach.
Step 4: Set aside tax as you go
Put a percentage of each payment aside for tax, a rough 20-30% of profit is a common starting point. A real-time tax estimate tells you the precise figure, so you’re never caught short in January.
How CleanBooksAI makes year one easy.
CleanBooksAI tracks income and expenses automatically, keeps a live tax estimate, and prepares your figures, so your first Self Assessment is a confirmation, not a cliff edge.
