How to avoid paying too much tax

A single wrong tax code can cost an employee more than £1,000 in overpaid tax across a full tax year, and many never notice ^[2]. Overpaid tax can be reclaimed for up to four years after the end of the tax year in which it arose, yet a large share of eligible refunds go unclaimed ^[3]. Paying the correct amount of tax, and no more, is largely a matter of checking a handful of things and claiming what the rules already allow.

Avoiding overpayment is not about aggressive schemes. It is about making sure the tax code is right, that every allowance the taxpayer is entitled to is applied, and that legitimate reliefs on pensions, work expenses and savings are actually claimed ^[7]. Each of these is built into the system for exactly this purpose, and each is routinely missed.

This guide walks through the practical steps in order of impact: checking and correcting the tax code, reclaiming past overpayments, claiming the main allowances and reliefs, and sheltering income that would otherwise be taxed. It is written for employees, employers and payroll administrators who want to make sure the right figure, and only the right figure, reaches HMRC.

Key takeaways

• A wrong or emergency tax code is the most common cause of overpaying, and it can be corrected mid-year through the tax code ^[2].
• Overpaid tax can be reclaimed for the current year and the four previous tax years ^[3].
• Marriage Allowance can cut a couple's tax by up to £252 a year where one partner has unused personal allowance ^[4].
• Pension contributions attract income tax relief at the taxpayer's marginal rate, and salary sacrifice adds a National Insurance saving ^[6].
• Job expenses such as uniforms, professional fees and working-from-home costs can be claimed as tax relief for up to four years ^[5].

Check the tax code first

The tax code is the single most important number on a payslip, because it tells the employer how much tax-free allowance to apply before deducting income tax ^[2]. A wrong code is the most frequent reason an employee overpays, and it is also the easiest to fix ^[1].

Spot a code that is costing money

The standard code for someone with a single job and the full allowance is 1257L, representing £12,570 of tax-free income ^[2]. Codes that often signal overpayment include BR, which taxes all income at the basic rate with no allowance, 0T, which gives no allowance at all, and any code ending in W1, M1 or X, which are emergency codes applied on a non-cumulative basis ^[14]. Emergency codes are common after starting a new job without a P45, and they can leave an employee without their full allowance until the code is corrected ^[14].

An employee can check the current code and how it was calculated through the personal tax account on GOV.UK, in the Check your Income Tax section ^[1]. Where the code is wrong, HMRC updates it and issues a revised code to the employer, who applies it on the next payslip ^[2]. Employers running an HMRC-recognised payroll platform apply the codes HMRC sends automatically, which is why a prompt correction feeds through quickly.

Reclaim tax already overpaid

Where the overpayment sits in the current tax year, HMRC usually corrects it by adjusting the code so the refund comes back through pay over the remaining months ^[1]. For earlier years, the taxpayer can claim through the personal tax account or by submitting the relevant form, with refunds typically issued within a few weeks ^[3]. The window is four years from the end of the tax year concerned, so a claim made now can still recover tax overpaid across several past years ^[3]. Keeping old payslips and P60s makes these claims straightforward, because they evidence the tax actually deducted ^[15].

Claim the allowances and reliefs already available

Beyond the personal allowance, several reliefs reduce a tax bill but only if they are claimed. They are not applied automatically, which is why they are so often left on the table ^[5].

Marriage Allowance

Marriage Allowance lets a lower-earning spouse or civil partner transfer £1,260 of their personal allowance to their partner, provided the lower earner has income below £12,570 and the higher earner is a basic-rate taxpayer ^[4]. The transfer reduces the couple's combined tax by up to £252 for the 2026-27 tax year ^[4]. A claim can also be backdated for up to four years where the couple was eligible, which can produce a lump-sum refund on top of the ongoing saving ^[4]. The claim is made online with a National Insurance number and proof of identity ^[4].

Tax relief on job expenses

An employee who pays for things needed to do their job can claim tax relief on them, and the relief is given at the rate of tax the person pays ^[5]. Qualifying costs include cleaning, repairing or replacing a uniform or protective clothing, tools bought for work, professional fees and subscriptions to approved bodies, and the extra household costs of working from home ^[5]. The relief cannot exceed the tax paid in the year, and any amount the employer has already reimbursed is excluded ^[13].

Claims can be made for the current tax year and the four previous years, so an employee who has never claimed can recover several years at once ^[5]. Sole traders account for these costs differently, through business expenses on their return rather than employment relief, which a payroll platform for small businesses keeps distinct from payrolled staff ^[13].

Use pensions to lower taxable income

Pension contributions are the most powerful legitimate way to reduce a tax bill, because the money paid in attracts tax relief and the taxable income falls accordingly ^[6].

Pension tax relief

Contributions to a registered pension attract income tax relief at the contributor's highest rate of tax ^[6]. A basic-rate taxpayer effectively gets £20 of relief for every £80 contributed, and a higher-rate taxpayer can claim back more through their tax return ^[6]. For earners caught in the 60% effective band between £100,000 and £125,140, where the personal allowance is withdrawn, a pension contribution can be worth substantially more than its face value because it can restore part of the lost allowance ^[7].

Salary sacrifice

Salary sacrifice takes the pension contribution from gross pay before income tax and National Insurance are calculated, so the employee saves both ^[6]. On a £1,000 sacrificed contribution, a basic-rate employee in the main National Insurance band saves £200 of income tax and £80 of employee National Insurance, and the employer normally avoids its 15% employer National Insurance on the sacrificed amount as well ^[8]. From 6 April 2029, only the first £2,000 of salary sacrificed into a pension each year will remain free of National Insurance, with amounts above that becoming liable, so the National Insurance advantage on larger contributions will narrow ^[8]. Employers setting up salary sacrifice need their payroll to handle the reduced gross correctly, which an HMRC-recognised payroll API does at the point of calculation.

Shelter savings and investment income

Income from savings and investments is taxed on top of earnings, but several allowances keep much of it out of tax if used deliberately ^[9].

Personal savings and dividend allowances

The personal savings allowance lets a basic-rate taxpayer earn £1,000 of interest tax-free each year, falling to £500 for higher-rate taxpayers and nothing for additional-rate taxpayers ^[9]. Separately, the first £500 of dividend income is covered by the dividend allowance before any dividend tax is due ^[11]. Because both allowances depend on the taxpayer's band, spreading savings and investments between partners can keep more income within the tax-free amounts ^[9].

Individual Savings Accounts

An Individual Savings Account shelters savings and investment returns from tax entirely, with no tax on the interest, dividends or gains inside it ^[10]. There is an annual subscription limit across all ISAs held, and using the allowance each year is one of the simplest ways to stop investment income from being taxed at all ^[10]. Unlike a pension, money in an ISA can be withdrawn at any time, which is why the two are often used together rather than as alternatives ^[10].

Other reliefs worth checking

Two further items are missed often enough to be worth a deliberate check, because both can move a taxpayer's position by a meaningful amount ^[16].

Gift Aid on donations

When a taxpayer donates to charity through Gift Aid, the charity reclaims basic-rate tax on the gift, and a higher or additional-rate taxpayer can claim the difference between their rate and the basic rate through their tax return ^[16]. For a higher-rate taxpayer, this means a £100 donation can carry personal tax relief of £25 on top of the amount the charity reclaims ^[16]. Like pension contributions, Gift Aid also extends the basic-rate band, which can pull income back out of the higher rate for people sitting just over a threshold ^[7]. The relief only works where the donor has paid at least as much tax as the charity reclaims, so records of donations matter ^[16].

Benefits in kind on the tax code

Taxable benefits such as a company car, private medical cover or an interest-free loan are usually collected by reducing the tax code, which lowers the tax-free allowance ^[17]. Where a benefit has ended or its value has fallen, an out-of-date code can keep deducting tax on a benefit the employee no longer receives ^[17]. Checking that the benefits reflected in the code still match reality is a quick way to stop a silent overpayment, and it is done through the same personal tax account used to check the code itself ^[1]. Employers that payroll benefits directly report them through payroll rather than the code, which an instant payslip generator reflects on the payslip ^[17].

Check the figures on any salary

The fastest way to confirm that the deductions on a payslip look right is to model the salary and compare. The Moonworkers tax code checker explains what a given code means for the personal allowance, and the UK salary calculator applies the 2026-27 income tax and National Insurance rules to any gross figure so an over-deduction stands out.

For employers, getting the deductions right at source is the other half of the equation, because an accurate payroll prevents the over-deductions that employees then have to reclaim ^[2]. Bureaux managing this across many clients often do so through a single multi-client payroll dashboard.

Conclusion

Avoiding overpayment comes down to attention rather than aggression. The tax code should be checked and corrected, past overpayments reclaimed within the four-year window, and every allowance the taxpayer qualifies for actually claimed rather than assumed ^[3]. Pensions, ISAs and the savings and dividend allowances then shelter the income that would otherwise drift into tax ^[6].

None of this steps outside the rules. Each measure is a relief or allowance HMRC has built into the system, waiting to be used. For employers, the counterpart duty is to deduct the right amount at source, because a correct payslip is the first line of defence against an employee ever overpaying in the first place.

Frequently asked questions

How do I know if I am on the wrong tax code?

Check the code on a recent payslip against the personal tax account on GOV.UK, which shows the current code and how it was worked out ^[1]. Codes such as BR, 0T, or any ending in W1, M1 or X often mean the full personal allowance is not being applied, which usually leads to overpaying ^[14]. If the code looks wrong, contacting HMRC prompts a corrected code to be issued to the employer, who then adjusts the next payslip ^[2].

How far back can overpaid tax be reclaimed?

Overpaid income tax can be reclaimed for the current tax year and the four previous tax years ^[3]. For the current year, HMRC often refunds through an adjusted tax code, so the money comes back through pay ^[1]. For earlier years, a claim through the personal tax account or the relevant form is usually paid within a few weeks, provided the taxpayer can evidence the tax deducted ^[3].

Do pension contributions really reduce tax?

Yes. Contributions to a registered pension attract income tax relief at the contributor's marginal rate, so a higher-rate taxpayer effectively pays less tax by contributing ^[6]. Where salary sacrifice is used, the contribution also escapes employee National Insurance, adding a further saving ^[6]. The relief is one of the reasons pensions are the most effective legitimate way to lower a tax bill, particularly for those in the 60% effective band above £100,000 ^[7].

Can an employee claim tax relief on working-from-home costs?

An employee can claim relief on the extra household costs incurred because they have to work from home, such as additional heating or business calls for the work area ^[5]. Costs that serve both private and work purposes, such as broadband or rent, cannot be claimed ^[5]. The claim covers the current year and the four previous years, and the relief is given at the employee's rate of tax, capped at the tax actually paid ^[13].