How to prepare for Self Assessment when self-employed

The deadline to file your 2025 to 2026 return online is 31 January 2027. That feels far away in November. It isn't, if your records are a mess. Here's how to prepare for Self Assessment so January is boring.

Know the dates first

GOV.UK's Self Assessment deadlines page gives these dates for the 2025 to 2026 tax year:

• 5 October 2026: the date to tell HMRC you need to file, if you haven't filed before.
• 31 October 2026: the deadline for a paper return.
• 30 December 2026: the date to file online if you want to pay through your tax code.
• 31 January 2027: the deadline to file online and to pay what you owe.

Miss the first one and you're already late to register. If that's you, do it today. Our guide to the UTR number explains what you'll need.

Step 1: Get your sign-in details sorted

GOV.UK's file your return page says you need your Unique Taxpayer Reference and your sign-in details. You may also be asked to prove your identity, which it says usually involves photo ID like a passport or driving licence.

Do this now, not on 30 January. Setting up an account can take time, and you don't want that stress on deadline day.

Step 2: Add up your income

Open your business bank account and list every payment from customers for 6 April 2025 to 5 April 2026. Match each one to an invoice. Anything without an invoice, find out why.

Say you're a tutor with eight regular families. With eight families paying monthly, one missed payment is easy to miss. A simple sheet with date, customer and amount shows the gap in minutes. If you need a routine for this, our piece on how to keep records has one.

Step 3: Add up your expenses

List what you spent on the business in the same period. Use receipts where you have them and bank statements where you don't. Tag anything unclear and decide later.

Don't guess at the end. If you're unsure what counts, read what expenses you can claim. If your income is small, check the trading allowance too. It might save you the work.

Step 4: Work out roughly what you'll owe

You don't need the exact figure yet. You need a ballpark, so the bill doesn't surprise you. Take your income, subtract your expenses, and you have your profit. Tax is worked out on profit, not on what you took in.

If you haven't been putting money aside, start with our guide to saving for tax. It shows a simple percentage method.

Step 5: Check for payments on account

GOV.UK's payments on account guidance says they are advance payments towards your next bill, including Class 4 National Insurance. Each payment is half of the tax you owed last year, due on 31 January and 31 July.

It also says you don't have to make them if last year's bill was under £1,000, or if you paid more than 80% of it outside Self Assessment. In your first year, the January bill can feel double, because it includes your first payment on account. Our explainer on payments on account covers that.

Step 6: Plan how you'll pay

GOV.UK's pay your bill page lists the options and the timing:

• Same or next day: online or telephone banking (Faster Payments), CHAPS, debit or corporate credit card online, or your bank or building society.
• 3 working days: Bacs, or Direct Debit if you've already set one up with HMRC.
• 5 working days: Direct Debit, if you haven't set one up before.

The page says the Post Office no longer takes payments. It also says you can pay in instalments before the deadline, weekly or monthly, if you prefer. That's a good one for tight cash flow. Pay a bit each month from now and the bill shrinks before January.

There's one more option. GOV.UK's pay through your tax code page says you can do this if you owe under £3,000, already pay tax through PAYE, and file online by 30 December. It doesn't suit most full-time sole traders, because they have no PAYE income. It helps if you have a job as well as a side business.

What happens if you're late

GOV.UK's penalties page says a late return gets:

• an initial penalty of £100
• £10 a day after 3 months, capped at £900
• an extra 5% of the tax due, or £300 if that's greater, after 6 months
• another 5% of the tax due, or £300 if greater, after 12 months

Late payment adds 5% of the unpaid tax at 30 days, 6 months and 12 months, plus interest. On its interest rates page, GOV.UK lists the late payment rate as 7.75% from 9 January 2026. Check that page for the current rate when you pay.

So a late return costs money even if you owe nothing. The £100 applies regardless.

A simple timeline

1. This week: check your UTR and sign-in details.
2. By end of November: list your income and match it to invoices.
3. By mid-December: list your expenses.
4. Before 30 December: file early if you want to use your tax code.
5. In January: file, then pay, using a method that arrives in time.

Filing early doesn't make you pay early. The payment date is still 31 January. But it gives you time to fix mistakes.

My take

Self Assessment isn't hard. Leaving it late is what hurts. Almost every problem I hear about comes down to records found in the last week. Spend an hour a week from now and you'll finish in an evening.

Part of that hour is knowing who has paid you. That's what we built Vcents for. You ask for payment in WhatsApp, and the bank transfer lands straight in your account, so your income is easy to match.

Sources

• GOV.UK: Self Assessment deadlines
• GOV.UK: Sign in and file your return
• GOV.UK: Self Assessment penalties
• GOV.UK: Pay your Self Assessment tax bill
• GOV.UK: Pay through your tax code
• GOV.UK: Payments on account
• GOV.UK: HMRC interest rates for late and early payments