Every year, thousands of taxpayers miss reporting income they didn’t realise counted — and that mistake often leads to unexpected tax bills or penalties.
If you file a Self-Assessment tax return, it’s crucial to understand what income you must declare to HMRC.
Whether you earn from employment, property, investments, or even crypto, every source has to be disclosed correctly.
In this guide, you’ll learn exactly which types of income to include, the deadlines that matter, and what happens if you don’t file on time.
Employment Income
If you’re employed and pay tax through PAYE, your employer already reports most of your income to HMRC.
However, you still need to include it in your Self-Assessment return — especially if you:
- Have multiple jobs or income from both employment and self-employment
- Receive benefits in kind, such as a company car or private healthcare
- Claim work-related expenses that aren’t reimbursed
Self-Employment and Freelance Income
If you earned more than £1,000 from self-employment during the tax year, you must declare it — even if it’s a side hustle or part-time venture.
This includes income from:
- Freelancing and consulting
- Selling goods or services online (eBay, Etsy, Depop, Shopify, etc.)
- Gig economy work like Uber, Deliveroo, or Fiverr
Importantly, you must declare your gross income, then deduct your allowable business expenses.
Rental and Property Income
Landlords must declare all rental income, including:
- Residential or commercial rent
- Holiday lets and Airbnb income
- Rent-a-Room income (beyond £7,500 per year)
You can claim related expenses such as letting fees, repairs, insurance, and mortgage interest (restricted relief applies).
Dividends, Investments, and Savings Income
Income from investments and dividends also counts. You need to report:
- Dividends from shares
- Interest from savings or bonds
- Income from peer-to-peer lending platforms
- Profits from share trading
Although some of this income benefits from allowances, like the Dividend Allowance (£500) and Personal Savings Allowance (£1,000), you must still include it in your tax return.
Foreign Income
If you live in the UK but earn money abroad, that income usually needs to be declared.
This includes overseas employment, rental income, or foreign dividends.
You might be eligible for Foreign Tax Credit Relief if you’ve already paid tax overseas, but you must still disclose the income first.
Capital Gains (Including Cryptoassets)
Whenever you sell or dispose of an asset for more than you paid, HMRC may charge Capital Gains Tax (CGT).
That includes:
- Property that’s not your main home
- Shares, stocks, and funds
- Cryptoassets such as Bitcoin or Ethereum
The annual exemption for 2025/26 is £3,000.
If your total gains exceed this, you must file a Self-Assessment return.
Other Income You Must Declare
There are a few less obvious income types that also count:
- Tips and commissions
- Cash-in-hand work
- Referral or affiliate income
- Crowdfunding or content creator earnings
- Inheritance income that generates interest or dividends
In short, if money came in and wasn’t already taxed, it probably belongs on your return.
Key Deadlines for Self-Assessment
It’s not enough to know what to declare — timing matters too.
Here are the dates you need to remember:
| Action | Deadline |
|---|---|
| Register for Self-Assessment (first-time filers) | 5 October 2025 |
| File Online Tax Return | 31 January 2026 |
| Pay Tax Owed | 31 January 2026 |
| Make Second Payment on Account (if applicable) | 31 July 2026 |
Penalties for Not Declaring or Filing Late
HMRC takes undeclared income seriously.
If you fail to file or underreport income, you may face:
- Automatic £100 late filing penalty (even if no tax is due)
- Daily fines of £10 after 3 months
- Up to £900 in additional penalties
- Interest on late payments
- Tax-geared penalties for deliberate or careless omissions
💡 Not registered yet?
If you’ve realised you need to file a Self-Assessment for the first time, you’ll need to register with HMRC before you can submit your return. It only takes a few minutes, but you’ll need your UTR (Unique Taxpayer Reference) first.
👉 Read our step-by-step guide on How to Register for Self-Assessment with HMRC to get started.
File your tax return with The Calculator Guy.
We can help you register with HMRC if required, explain you your tax liabilities, prepare and submit returns accurately and on time.