How to prepare for your first Self Assessment tax return: a practical checklist

Your first Self Assessment return is much easier if you gather records before logging into HMRC. The goal is to know your income, expenses, profit, tax estimate, and payment deadlines before you start typing numbers into the return.

1. Confirm the tax year you are filing

UK tax years run from 6 April to 5 April. The return due by 31 January usually covers the tax year that ended the previous 5 April. Check the dates before gathering records so you do not mix two years together.

2. Gather income records

Sales invoices and receipts.
Bank statements showing customer payments.
Payment processor reports from Stripe, PayPal, marketplaces, or booking platforms.
CIS statements if you work in construction.
PAYE P60 or P45 forms if you also had employment income.

3. Review expenses

Gather receipts and statements for software, travel, mileage, office costs, equipment, professional fees, insurance, and home-office costs. If you are unsure what counts, read what expenses sole traders can claim before finalising the profit figure.

4. Separate business and personal spending

Mixed costs like phone, broadband, home office, and vehicle use need a reasonable business split. Write down the method you used. A note made now is much easier to defend than trying to remember the logic years later.

5. Choose or confirm your accounting basis

Cash basis often follows money received and paid. Traditional accounting can include income and expenses when earned or incurred, even if payment happens later. Read cash basis vs traditional accounting if unpaid invoices or supplier bills cross the year end.

6. Estimate the tax before filing

Once you know profit, run it through the self-employed tax calculator. If you also had PAYE income, add it in the optional second field so the tax bands apply to combined income.

7. Check payments on account

Your first Self Assessment bill can feel larger than expected because HMRC may ask for the balancing payment plus the first payment on account for the next tax year. Read the payments on account guide before assuming the January figure is only last year's tax.

8. Avoid common first-return mistakes

Entering turnover where HMRC asks for profit.
Forgetting PAYE income, bank interest, or other taxable income.
Claiming personal costs as business expenses.
Missing student loan or pension contribution details.
Leaving the return until 31 January and then discovering missing records.

9. Keep the records after filing

Filing the return is not the end of the admin. Keep supporting records in case HMRC asks questions later. The record-keeping guide explains what to keep and for how long.

10. Plan next year immediately

After filing, set up a simple monthly routine: update records, estimate profit, and move tax money into a separate savings account. The weekly tax set-aside calculator can help turn that into a habit.

Official source

GOV.UK's Self Assessment starting point is here: Self Assessment tax returns. Deadlines are here: Self Assessment deadlines.