You've built a side income. Maybe it's rent from a spare room, royalties from an ebook, dividends from shares, or a small online shop ticking over in the background. The money arrives whether you're working or not, which is great. The bit that trips people up is what HMRC expects in return.
Here's the honest answer: most passive income is taxable, and "I earned it while I slept" is not a defence. The good news is there are real tax-free allowances, and once you know which ones apply to you, the rules are manageable.
This guide explains how the main types of passive income are taxed for the 2025/26 tax year, when you have to register for Self Assessment, and the figures that decide how much you'll pay. It's written for UK business owners, landlords and sole traders weighing up extra income streams.
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Is passive income taxable in the UK?
In most cases, yes. The label "passive" describes how the money is earned, not how it's taxed. HMRC cares about the type of income, not the effort behind it.
The main exception is income held inside a tax wrapper. Interest, dividends and gains earned inside an ISA are tax-free, which is the whole point of an ISA. Almost everything else, rental profit, business profit from an online shop or course, royalties, and dividends or interest held outside a wrapper, can be taxable once you go over the relevant allowance.
The amount of tax depends on three things: the type of income, how much you earn from it, and your total income from all sources. Your tax-free personal allowance of £12,570 for 2025/26 applies across your whole income, so a side income stacked on top of a salary is taxed at your highest band.
What is the trading allowance?
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The trading allowance lets you earn up to £1,000 a year (gross, before expenses) from trading or casual self-employment without paying tax on it or, in many cases, without needing to tell HMRC at all. It covers things like ebook royalties, online course sales, freelance odd jobs, and small ecommerce takings.
There's a separate £1,000 property allowance that works the same way for property income such as renting out a driveway or storage space.
If your gross income from these activities is £1,000 or less in the tax year, you usually don't need to report it. Go over £1,000 and you'll generally need to register for Self Assessment and either claim the £1,000 allowance instead of your actual expenses, or deduct your actual expenses, whichever leaves you better off.
| Allowance | Amount (2025/26) | Covers |
|---|---|---|
| Trading allowance | £1,000 | Self-employment, casual and miscellaneous income |
| Property allowance | £1,000 | Land and property income |
How is rental income taxed?
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Rental profit from a buy-to-let or other let property is taxable income. You add your rental profit (rent received less allowable expenses) to your other income and pay tax at your marginal rate: 20% in the basic-rate band, 40% in the higher-rate band, and 45% in the additional-rate band for 2025/26.
A few points landlords get caught out by:
- Mortgage interest isn't deducted as a straight expense. Instead you get a basic-rate (20%) tax credit on finance costs.
- Rental profit doesn't attract National Insurance, because letting property normally isn't treated as a trade.
- You report rental profit through Self Assessment once it's above the £1,000 property allowance.
If you let property, our Self Assessment service and landlord accounting pages set out how we handle this. From 6 April 2026, Making Tax Digital for Income Tax also starts to apply to landlords and sole traders with qualifying income over £50,000, so it's worth getting your record-keeping in order now.
How is the rent-a-room scheme taxed?
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If you let a furnished room in your own home, the Rent a Room Scheme lets you earn up to £7,500 a year tax-free. The threshold halves to £3,750 if you share the income with someone else, such as a partner.
If your gross receipts are £7,500 or less, the relief is automatic and you don't need to do anything. Go over £7,500 and you have a choice: pay tax on the amount above £7,500, or pay tax on your actual profit (rent less expenses) in the normal way, whichever gives the lower bill.
How are dividends taxed?
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Dividends from shares held outside an ISA are taxable, but you get a dividend allowance first. For 2025/26 the dividend allowance is £500, so the first £500 of dividends is tax-free.
Above that, dividends are taxed at rates that depend on your income band:
| Band | Dividend rate (2025/26) |
|---|---|
| Basic rate | 8.75% |
| Higher rate | 33.75% |
| Additional rate | 39.35% |
Dividends are treated as the top slice of your income, so the rate you pay depends on where they sit once stacked on your other income. If you take dividends from your own company, our dividend tax calculator gives you a quick estimate.
How is interest and savings income taxed?
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Interest from ordinary savings (outside an ISA) can be taxable, but most people have a Personal Savings Allowance that shelters a chunk of it. The exact allowance depends on your tax band. Interest inside a cash ISA or stocks and shares ISA stays tax-free.
Because the Personal Savings Allowance and the starting rate for savings interact with your other income, it's the one area where a quick check with an accountant often pays for itself if you have meaningful savings income.
Do I pay Capital Gains Tax on passive income?
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Capital Gains Tax (CGT) applies when you sell or dispose of an asset for more than you paid, for example shares held outside an ISA, or a second property. It's a tax on the gain, not the whole sale price.
For 2025/26 you have an Annual Exempt Amount of £3,000. Gains above that are taxed as follows:
| Asset type | Basic-rate band | Higher/additional band |
|---|---|---|
| Most assets (e.g. shares) | 18% | 24% |
| Residential property | 18% | 24% |
These are the rates that apply from 30 October 2024 for most assets, following the change announced at the Autumn 2024 Budget. Gains inside an ISA are exempt from CGT entirely. You can sanity-check a disposal with our Capital Gains Tax calculator.
Do I pay National Insurance on passive income?
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It depends on whether HMRC treats the activity as a trade.
If your side income is genuine self-employment, an online shop, freelance work, selling courses, you may pay Class 4 National Insurance. For 2025/26 that's 6% on profits between £12,570 and £50,270, and 2% on profits above £50,270.
Investment income behaves differently. Dividends, savings interest and rental profit don't attract National Insurance, only Income Tax where it's due. That distinction matters when you're deciding how to structure a new income stream, and it's one of the things we look at in tax advisory.
When do I need to register for Self Assessment?
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As a general rule, you need to register for Self Assessment if any of the following apply for the tax year:
- Your gross trading income is over the £1,000 trading allowance.
- Your gross property income is over the £1,000 property allowance.
- You have dividends or other untaxed income to report that takes you over an allowance.
- You have a Capital Gains Tax liability to declare.
The deadlines are fixed. You must register by 5 October following the end of the tax year, file your online return by midnight on 31 January, and pay any tax due by the same 31 January date. Miss them and HMRC charges penalties and interest.
An illustrative example
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Illustrative example. Sam is an employed graphic designer in the basic-rate band. Alongside their salary they earn £2,400 of ebook royalties and £1,800 of dividends from shares held outside an ISA in 2025/26. They have no allowable expenses worth claiming on the royalties.
- Ebook royalties: £2,400 is over the £1,000 trading allowance, so they register for Self Assessment. They claim the £1,000 trading allowance instead of expenses, leaving £1,400 taxable at their 20% basic rate. Tax: £1,400 x 20% = £280.
- Dividends: the first £500 is covered by the dividend allowance. The remaining £1,300 is taxed at the basic-rate dividend rate of 8.75%. Tax: £1,300 x 8.75% = £113.75.
- National Insurance: their ebook profit is below the £12,570 Class 4 starting point, so no Class 4 NIC is due on it. Dividends never attract NIC.
Total extra tax for the year: £280 + £113.75 = £393.75, reported and paid through Self Assessment by 31 January following the tax year.
Figures use 2025/26 rates and assume Sam stays within the basic-rate band once the side income is added. Your own position will differ.
Want help getting your side income right?
If you're earning income on the side and you're not sure what's taxable, what to report, or how to keep more of it, we can help. Book a free 20-minute call with a Zmartly accountant and we'll walk through your income streams and set up clean record-keeping before the next deadline. Visit zmartly.co.uk/contact to get started.
Frequently asked questions
Is passive income taxable in the UK?
Most passive income is taxable. The main exception is income held inside an ISA, where interest, dividends and gains are tax-free. Rental profit, business profit from online activities, royalties, and dividends or interest held outside a wrapper can all be taxable once you exceed the relevant allowance. The tax depends on the type of income and your total income for the year.
How much can I earn before I pay tax on side income?
You can earn up to £1,000 of gross trading income and a separate £1,000 of gross property income each tax year tax-free under the trading and property allowances for 2025/26. The Rent a Room Scheme allows up to £7,500 a year tax-free from letting a furnished room in your own home. Above these amounts the income is generally taxable and reportable.
Do I need to register for Self Assessment for passive income?
You generally need to register for Self Assessment if your gross trading income is over £1,000, your gross property income is over £1,000, you have untaxed income that exceeds an allowance, or you have a Capital Gains Tax liability to declare. You must register by 5 October following the end of the tax year and file your online return by 31 January.
How are dividends taxed outside an ISA in 2025/26?
For 2025/26 the first £500 of dividends is tax-free under the dividend allowance. Above that, dividends are taxed at 8.75% for basic-rate taxpayers, 33.75% for higher-rate taxpayers, and 39.35% for additional-rate taxpayers. Dividends held inside an ISA are tax-free.
Do I pay National Insurance on rental or investment income?
No. Rental profit, dividends and savings interest don't attract National Insurance, only Income Tax where it's due. National Insurance (Class 4) applies to self-employment profit, such as a genuine trade like an online shop or freelance work, at 6% on profits between £12,570 and £50,270 and 2% above £50,270 for 2025/26.
Do I pay Capital Gains Tax when I sell investments?
You may, if your total gains for the year exceed the Annual Exempt Amount of £3,000 for 2025/26. Gains above that on most assets, such as shares held outside an ISA, are taxed at 18% in the basic-rate band and 24% in the higher or additional band. Residential property gains are also taxed at 18% and 24%. Gains inside an ISA are exempt.
