Self Assessment countdown: a six-week plan

By The Income Tracker · Updated 16 September 2026 · 6 min read

The dates that matter

Miss the filing date and there is an automatic £100 penalty, even if you owe nothing. After three months it becomes £10 a day for up to 90 days, with further penalties at six and twelve months. Late tax attracts interest from 1 February and a 5% surcharge once it is 30 days late.

Week by week

1. Week 1: register, or find your login. New to Self Assessment? Register on GOV.UK now; the Unique Taxpayer Reference arrives by post and takes up to ten working days. Already registered? Confirm your Government Gateway login works and note your UTR.
2. Week 2: export the year. Download transactions from 6 April 2025 to 5 April 2026 from every business account as CSV files. Most banks let you set a custom range; some cap it at 12 or 18 months, so do it now rather than in January.
3. Week 3: categorise. Import the files into The Income Tracker and put every business row under one of HMRC's expense headings (below). The app remembers each supplier, so the second pass is fast.
4. Week 4: gather the rest. P60 or P45 from any employment, bank interest, dividends, rental income, pension contributions, Gift Aid donations, student loan plan, and any Child Benefit if income is over £60,000.
5. Week 5: check payments on account. If last year's bill was over £1,000 and less than 80% of it was collected at source, HMRC expects two advance payments for the next year. Your January payment may be the balance plus half of next year's estimate.
6. Week 6: file. Do it in December or early January rather than on the 31st, when the site is slow and mistakes are expensive. Pay by bank transfer, debit card or Direct Debit; card payments take time to clear.

HMRC's expense headings

The self-employment pages group expenses under fixed headings. Use the same names as categories in your tracker and the return fills itself in.

• Cost of goods bought for resale or goods used
• Car, van and travel expenses
• Wages, salaries and other staff costs
• Rent, rates, power and insurance costs
• Repairs and maintenance of property and equipment
• Phone, fax, stationery and other office costs
• Advertising and business entertainment costs (entertainment is not allowable)
• Interest on bank and other loans
• Bank, credit card and other financial charges
• Accountancy, legal and other professional fees
• Other business expenses

Simplified expenses: sometimes easier

Sole traders can use flat rates instead of actual costs for three things: vehicles (45p a mile for the first 10,000 business miles, 25p after), working from home (£10, £18 or £26 a month depending on hours), and living at your business premises. Flat rates save receipts but are not always the cheaper choice, so work both out once.

Frequently asked questions

When is the Self Assessment deadline for the 2025/26 tax year?

Online returns and payment are due by 31 January 2027. Paper returns by 31 October 2026. First-time filers must register by 5 October 2026.

What is the penalty for filing late?

£100 immediately, then £10 a day after three months for up to 90 days, with further penalties at six and twelve months. Late payment adds interest and a 5% surcharge after 30 days.

What records do I need for Self Assessment?

Dated records of all business income and expenses with receipts and bank statements, plus P60s, interest, dividend and pension figures. Keep them for at least five years after the filing deadline.

Can The Income Tracker submit my return?

No. It is a free tracker for seeing income, expenses and what to set aside. You file through HMRC's website or recognised software; the categorised totals from the tracker go straight into the boxes.

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