Skip to content

Taxation (UK) · The overall function and purpose of taxation in a modern economy

Tax Incentives: ISAs and Rent-a-Room Relief in TX-UK

Updated 11 October 2026 · Fact-checked

Governments use tax incentives to change behaviour. An ISA lets you save or invest up to £20,000 a year with tax-free returns, which encourages saving. Rent-a-room relief exempts rental income from a furnished room in your own home up to £7,500, which encourages letting spare rooms.

Understand Tax Incentives: ISAs and Rent-a-Room Relief

A tax is not only a way to raise money. Governments also use tax to steer behaviour. A relief that lowers tax on an activity makes that activity cheaper, so people do more of it. This is the incentive function of taxation, and it is one of the purposes of tax that TX-UK expects you to explain.

The individual savings account (ISA) is an incentive to save. Income and gains inside an ISA are free of tax. The overall investment limit is £20,000. You can split that between types of ISA, such as cash, stocks and shares, or lifetime ISA. The tax tables give you the overall limit only, so do not quote sub-limits for individual types unless the question provides them.

Rent-a-room relief is an incentive to let spare rooms in your own home. It is a property income exemption. The limit is £7,500. If your gross receipts from letting furnished accommodation in your only or main home are at or below the limit, the income is exempt. This also helps housing supply by making lodgers more attractive.

If receipts are above £7,500, you have two choices. Under the normal rules you are taxed on receipts less actual expenses. Under the alternative method you are taxed on receipts less £7,500, with no expenses deducted. The taxpayer picks whichever gives the lower profit.

When the exam asks you to explain how an incentive influences behaviour, give three parts: what the relief is, the limit, and the behaviour it aims to change.

Key rules to remember

ISA overall investment limit
Overall limit = £20,000 per tax year
Income and gains inside an ISA are exempt from tax. The limit applies to total subscriptions across all ISA types.
Rent-a-room limit
Exempt if gross receipts ≤ £7,500
Applies to furnished accommodation in your own home. If receipts are within the limit, there is no taxable property income.
Rent-a-room above the limit: alternative method
Taxable amount = Gross receipts − £7,500
No expenses are deducted. Compare with the normal method: receipts − actual expenses. Use the lower figure.
Purpose of incentive reliefs
Relief → cheaper activity → more of the activity
ISA encourages saving. Rent-a-room encourages letting spare rooms.

How to solve Tax Incentives: ISAs and Rent-a-Room Relief questions

Use this method for any question on ISAs or rent-a-room relief, whether it is an objective test or a written part.

  1. 1Identify which relief the question is about: ISA or rent-a-room.
  2. 2State the limit from the tax tables: £20,000 for ISAs, £7,500 for rent-a-room.
  3. 3For ISAs, check the amount subscribed against £20,000. Income and gains inside the ISA are not taxable, so exclude them from the computation.
  4. 4For rent-a-room, compare gross receipts (not profit) with £7,500. If receipts are at or below the limit, the income is exempt.
  5. 5If receipts exceed £7,500, work out the normal method (receipts − expenses) and the alternative method (receipts − £7,500). Choose the lower taxable figure.
  6. 6If asked how the relief influences behaviour, name the behaviour encouraged: saving or letting rooms.
  7. 7Write the final figure clearly and state the taxable amount or the exempt amount as asked.

Quickest way: Limit test, then compare

When to use it: Use in Section A or Section B objective questions where you must decide quickly whether income is exempt or which method is better.

  1. Write the limit next to the question: £20,000 or £7,500.
  2. Rent-a-room: compare gross receipts with £7,500. At or below means taxable income is nil.
  3. If above, compute receipts − £7,500 and receipts − expenses. Pick the smaller.
  4. ISA: if the question asks about tax on interest or gains inside an ISA, the answer is nil.
  5. Check that your chosen answer matches the exact wording, such as taxable or exempt.

Common mistakes in Tax Incentives: ISAs and Rent-a-Room Relief

  • Comparing rent-a-room profit, not gross receipts, with £7,500.

    Students are used to taxing profit after expenses.

    Fix: The exemption test uses gross receipts. Only above the limit do expenses matter.

  • Deducting expenses as well as £7,500 under the alternative method.

    Students combine the two methods.

    Fix: The alternative method is receipts − £7,500 only. Expenses are ignored.

  • Taxing income and gains earned inside an ISA.

    Students treat ISA interest like normal savings income.

    Fix: Returns inside an ISA are exempt, so leave them out of the income tax computation.

  • Quoting a wrong ISA limit or inventing sub-limits.

    Students remember figures from other years or sources.

    Fix: Use the Finance Act 2025 tables: the overall investment limit is £20,000.

  • Applying rent-a-room relief to a let of a separate property.

    Students forget the relief is for furnished accommodation in the owner's own home.

    Fix: Check that the room is in the taxpayer's main home. A let of another property is normal property income.

  • Explaining incentives without naming the behaviour.

    Students describe the relief but skip the purpose.

    Fix: Always finish with the aim: encourage saving, or encourage the letting of spare rooms.

Worked examples

Example 1

Priya lets a furnished room in her main home for the whole tax year and receives £6,200. Her expenses are £1,400. Calculate her taxable property income.

Show the solution
  1. Identify the relief: rent-a-room, with a limit of £7,500.
  2. Compare gross receipts of £6,200 with £7,500.
  3. £6,200 is below the limit, so the income is exempt.
  4. Expenses are irrelevant when the relief applies in full.

Answer: Taxable property income is nil.

Example 2

Tom lets a furnished room in his main home and receives £10,000 in the tax year. His allowable expenses are £1,500. Calculate the lower taxable amount available to him.

Show the solution
  1. Gross receipts of £10,000 exceed the £7,500 limit, so the income is not fully exempt.
  2. Normal method: £10,000 − £1,500 = £8,500.
  3. Alternative method: £10,000 − £7,500 = £2,500. No expenses are deducted.
  4. The alternative method gives the lower figure, £2,500, so Tom would choose it.

Answer: Taxable amount is £2,500 using the alternative method.

Exam tips

  • Memorise two figures: £20,000 for the ISA overall limit and £7,500 for rent-a-room. Both appear in the tax tables, but know them before the exam.
  • In written answers on tax purposes, link each relief to a behaviour: ISAs encourage saving, rent-a-room encourages letting rooms.
  • In rent-a-room questions, calculate both methods when receipts exceed £7,500, then state which is lower.
  • In objective tests, read whether the question asks for exempt income, taxable income or the tax saved. Answers are all or nothing.
  • Show workings clearly in Section C so marks are available even if a figure is wrong.

Practice questions from The overall function and purpose of taxation in a modern economy

Tax Incentives: ISAs and Rent-a-Room Relief in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Tax Incentives: ISAs and Rent-a-Room Relief: frequently asked questions

What is the ISA limit in ACCA TX-UK?

For the Finance Act 2025 tables, the overall ISA investment limit is £20,000. You can spread it across ISA types. Returns inside the ISA are free of tax.

What is the rent-a-room relief limit?

It is £7,500. If gross receipts from letting furnished accommodation in your own home are at or below this, the income is exempt. Above it, you can choose between the normal method and the alternative method.

How does rent-a-room relief work above the limit?

You compare two figures. The normal method taxes receipts less actual expenses. The alternative method taxes receipts less £7,500 with no expenses. You choose whichever gives the lower taxable amount.

How do tax incentives influence behaviour?

A relief reduces the tax cost of an activity, so people are more likely to do it. ISAs make saving more attractive. Rent-a-room relief makes letting a spare room more attractive.