Your First Self Assessment / Lesson 6 of 7
Registering and filing
The form has dozens of sections. You will probably need four of them.
The short answer
- ✓ Register by 5 October and allow weeks for the UTR and activation code
- ✓ Answering the tailoring questions honestly hides most of the form
- ✓ Your P60 supplies the employment figures; add a P45 if you changed jobs
- ✓ Read the calculation before submitting: payments on account appear there
The timeline
Register with HMRC by 5 October after the tax year ends
UTR arrives by post around 10 working days
Activation code arrives a few days after that
File online by 31 January
Pay by 31 JanuaryTwo posted letters stand between registering and being able to file. That is why registering in January is a genuine risk rather than a technicality.
Tailoring the return
The online return opens by asking which types of income apply to you. Answer honestly and everything irrelevant disappears. A typical employee with one side income needs:
- Employment, filled in from your P60
- Self-employment, or property, or wherever the extra income belongs
- Tax reliefs, for pension contributions and Gift Aid
- Check and submit
That is four sections out of a form that looks like forty.
Your P60 does the heavy lifting
The employment section wants your pay and the tax deducted, both of which are on your P60. Copy them across exactly. If you changed jobs during the year you will need the P45 from the old job as well, and both must be included.
Reliefs people forget
| Relief | Who misses it |
|---|---|
| Higher-rate pension relief | Anyone on a relief-at-source scheme paying higher rate |
| Gift Aid donations | Higher-rate taxpayers, who can claim the difference |
| Employment expenses | Anyone who has not claimed them separately |
| Marriage Allowance | Couples where one earns under the personal allowance |
The bit HMRC does not spell out
Read the calculation HMRC shows you before submitting. It sets out exactly how the bill was arrived at, and it is where a payment on account first appears if your liability has crossed £1,000. People submit without reading, then get a January demand half as large again as they expected, having been shown it in advance.
Common mistakes
- Registering too late to receive a UTR in time. Two posted letters take weeks.
- Skipping the tailoring questions. They are what shrinks the form.
- Forgetting a mid-year job change. Both employments must be included.
- Not reading the calculation. Payments on account are announced there.
Try it on your own numbers
This is the same calculator as the full tool page, using 2026/27 rates.
About you and your income
Tell us where you live and how you earned money - we only ask about the sources you tick.
Which of these did you have in the tax year? (tick all that apply)
Your income for the year
Use your P60/P45, business records, dividend vouchers and bank statements. Whole-year totals, before tax.
Employment (PAYE)
Self-employment
UK property
Dividends
Savings interest
Capital gains
The first of gains is exempt. We apply in your basic-rate room and above it.
Expenses, allowances & reliefs
These reduce your bill - don't skip them. Not sure what you can claim? Run the expenses checker first.
Self-employment expenses
Best when your real expenses are under £1,000. You can't claim both.
Property expenses
Estimated bill so far
Total liability minus already collected at source. Calculated with 2026/27 rates.
This is an estimate and organiser, not tax advice, and nothing is sent to HMRC - confirm every figure on GOV.UK before you file.
- Total income
- Personal Allowance (tapered - income over £100k)
- Income Tax
- Class 4 National Insurance
- High Income Child Benefit Charge
- Student loan due via Self Assessment
- Capital Gains Tax
- Total liability
- Less PAYE / CIS already paid
Your profit is under the £ small profits threshold - you can pay voluntary Class 2 NI (£/week) to protect your State Pension record. Not added to this bill.
When you'd pay (31 January after the tax year ends, then 31 July)
- 31 January - balancing payment
- 31 January - 1st payment on account
- 31 July - 2nd payment on account
- Total due on 31 January
What goes where on your return
| Form / section | What to enter | Your figure |
|---|---|---|
Box numbers follow the current SA forms and can move slightly year to year - always match the description printed on the form or online screen you're completing.
Saved scenarios
| Scenario | Liability | Balance due | |
|---|---|---|---|
Key takeaways
- ✓ Register by 5 October and allow weeks for the UTR and activation code
- ✓ Answering the tailoring questions honestly hides most of the form
- ✓ Your P60 supplies the employment figures; add a P45 if you changed jobs
- ✓ Read the calculation before submitting: payments on account appear there
Check you have got it
3 quick questions. No score is kept, and you can change your mind.
1. Why is registering in January risky?
2. You changed jobs mid-year. What do you need?
3. Where does a payment on account first appear?
Sources
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