Self Assessment (SA100).

You may need to file a Self Assessment tax return if you:​

• Are self-employed as a sole trader and earned more than £1,000 before expenses.​

• Are a partner in a business partnership.​

• Have income from property rental.​

• Receive untaxed income, such as tips or commission, of £2,500 or more.​

• Have savings or investment income of £10,000 or more before tax.​

• Need to pay Capital Gains Tax on profits from selling assets.​

Penalties for late filing include:​

• Missed filing deadline: An initial £100 penalty.

• Three months late: Daily penalties of £10, up to a maximum of £900.​

• Six months late: An additional £300 or 5% of the tax due, whichever is higher.​

Penalties for late payment include:​

• 30 days late: 5% of the tax unpaid at that date.​

• Six months late: An additional 5% of the tax unpaid.​

• Twelve months late: A further 5% of the tax unpaid.​

Interest is also charged on late payments.

You can file your tax return:​

• Online: Through the HMRC website.

• By paper: Using the SA100 form, if you meet specific criteria.​

Filing online is generally faster and provides immediate confirmation of receipt.

Key deadlines include:​

• 5 October: Register for Self Assessment if you’re a new filer.

• 31 October: Submit paper tax returns for the previous tax year.

• 31 January: Submit online tax returns and pay any tax owed for the previous tax year.​

Missing these deadlines can result in penalties and interest charges.

Maintaining accurate records is essential. You should keep:​

• Income records: Invoices, bank statements, and sales records.​

• Expense records: Receipts for business expenses, utility bills, and other allowable costs.​

• Other relevant documents: P60s, P45s, and details of any other income.​

HMRC requires you to retain these records for at least five years after the 31 January submission deadline of the relevant tax year.

If you’re filing a Self Assessment tax return for the first time, you must register with HMRC. The registration process depends on your circumstances:​

• Self-employed or sole trader: Register using form CWF1.

• Not self-employed: Register using form SA1.​

• Partner in a partnership: Register using form SA401.​

After registering, HMRC will issue you a Unique Taxpayer Reference (UTR) number, which you’ll need to file your tax return.