28 April 2026 · 8 min read · Bruce Thomas
Self Assessment is the system HMRC uses to collect tax that is not deducted at source. If your income comes only through PAYE with no complications, you probably do not need to file at all.
Who usually needs to file
- The self-employed and members of partnerships
- Landlords with property income above the reporting limits
- Company directors with dividend income to declare
- People with untaxed income such as investments or foreign income
- Higher earners affected by the High Income Child Benefit Charge
- Anyone with capital gains to report
Key dates
The tax year runs to 5 April. Online returns and the balancing payment are due by the following 31 January, with a second payment on account due 31 July. Register by 5 October following the tax year if you are filing for the first time.
Filing early does not mean paying early. Submitting in June still leaves payment due in January — but you know the number seven months ahead.
Payments on account
Where your liability exceeds a modest threshold and most of it is not collected at source, HMRC asks for payments on account towards the next year, each equal to half the current liability.
This is why the first profitable year hurts: January can include the balancing payment plus a first payment on account — effectively one and a half years of tax at once.
What to gather
- Business income and expense records, or accounts if prepared
- P60, P45 and P11D from any employment
- Bank and investment interest, and dividend vouchers
- Rental income and property expense records
- Pension contributions and gift aid donations
- CIS deduction statements if you are a subcontractor
- Details of any capital disposals during the year
Common mistakes
- Forgetting the July payment on account
- Omitting pension contributions and losing higher-rate relief
- Claiming round-sum amounts with nothing to support them
- Missing the separate 60-day deadline for residential property gains
- Leaving it until late January, when there is no time to check anything
Penalties
A late return attracts an immediate fixed penalty, with further penalties as the delay grows, and interest runs on unpaid tax. If you cannot pay, contact HMRC or your accountant early — a time to pay arrangement is far better than silence.
This article is general guidance for business owners in the UK and does not amount to advice for your particular circumstances. Tax rules change and the right answer depends on your figures — please take specific advice before acting.
