Legal ways to reduce UK tax: maximise pension contributions (which reduce taxable income at your marginal rate); use the full £20,000 ISA allowance (sheltering investment and savings returns permanently); claim the Marriage Allowance if one partner earns below £12,570 (worth up to £252/year, backdatable 4 years); claim all allowable business expenses if self-employed; and use the £3,000 CGT Annual Exempt Amount each year rather than letting gains accumulate. None of these require aggressive tax planning — all are explicitly designed by Parliament for this purpose.
There's a meaningful distinction between tax avoidance and tax evasion — one is legal and sensible, the other is criminal. Using allowances and reliefs that Parliament has specifically designed for ordinary people is not aggressive tax avoidance; it's good financial planning. Here's what's actually available and how to use it.
1. Maximise Pension Contributions
This is one of the most powerful and consistently underused tax reliefs available. Pension contributions attract tax relief at your marginal rate: a basic-rate taxpayer pays only £80 for each £100 deposited in a pension (HMRC adds £20). A higher-rate taxpayer effectively pays only £60 (with the additional 20% claimed through Self Assessment).
Annual limit: £60,000 or 100% of earnings, whichever is lower. This is genuinely large — even professional earners typically can't come close to maxing it. Contributing more than you currently do — particularly if you pay higher-rate tax — is nearly always financially advantageous.
2. Use the Full ISA Allowance
The £20,000 annual ISA allowance shelters savings interest, investment returns, and dividends from tax permanently. With dividend tax rates having increased in April 2026, and CGT allowances having been cut dramatically from £12,300 to £3,000 in recent years, the ISA wrapper is more valuable than it's been in a decade.
Using unused allowance is particularly important before April 2027, when the Cash ISA allowance for under-65s reduces to £12,000.
3. Claim the Marriage Allowance
If one partner earns below £12,570 and the other is a basic-rate taxpayer, the lower earner can transfer £1,260 of their Personal Allowance — saving the couple up to £252/year and backdatable up to four tax years. Many eligible couples have never claimed it. See our detailed guide on the Marriage Allowance for eligibility criteria and how to apply.
4. Claim All Allowable Business Expenses
Self-employed sole traders who under-claim expenses pay tax on income they shouldn't. Common under-claimed categories: home working costs, business proportion of phone and internet, professional development, software, and business travel mileage. Each £100 of unclaimed expenses costs a basic-rate taxpayer £20 in avoidable tax; a higher-rate taxpayer £40.
5. Use CGT Annual Exempt Amount Every Year
The £3,000 Annual Exempt Amount for Capital Gains Tax doesn't carry forward — use it or lose it. Realising gains up to £3,000 each tax year (rather than letting gains accumulate for a single large disposal years later) is more tax-efficient over time. Transfers between spouses are CGT-free, doubling the effective allowance to £6,000 for couples.
6. Salary Sacrifice for NI Savings
Where employers offer salary sacrifice for pension contributions, both employer and employee avoid NI on the sacrificed amount. An employee contributing £100/month to a pension through salary sacrifice saves approximately £8/month in NI (at 8% NI rate) compared with contributing the same £100 from take-home pay. The employer saves too — well-run schemes often redirect employer NI savings back into the pension pot.
Frequently Asked Questions
Is tax avoidance legal?
Using allowances Parliament has created for ordinary taxpayers is completely legal and entirely different from the aggressive artificial schemes (marketed by some advisers) that HMRC actively challenges. Pension contributions, ISAs, Marriage Allowance, and claiming allowable business expenses are the mainstream of legitimate tax planning.
How does higher-rate pension relief work?
Basic-rate relief (20%) is added automatically to pension contributions. Higher-rate taxpayers can claim the additional 20% through Self Assessment. Many higher-rate taxpayers who contribute to personal pensions forget to claim this additional relief — it's worth checking.
For HMRC's guidance on income tax reliefs, visit gov.uk/income-tax-reliefs.
