Understanding the UK Tax System in 2024/25
The UK tax system can feel complex, but it is built around a relatively straightforward set of principles. Most working people pay two main taxes on their earnings: income tax and National Insurance contributions. Both are collected automatically through the PAYE (Pay As You Earn) system for employees, while the self-employed pay through Self Assessment. Understanding how these taxes interact — and how to legitimately reduce your tax bill — is one of the most valuable pieces of financial knowledge you can have.
The 2024/25 Tax Year: What Changed?
The 2024/25 tax year (6 April 2024 to 5 April 2025) saw one significant change: the main employee National Insurance rate was cut from 10% to 8% in April 2024, following an earlier cut from 12% to 10% in January 2024. This means employees are now paying 4 percentage points less NI on earnings between £12,570 and £50,270 than they were in 2023/24. For someone earning £35,000, this represents a saving of approximately £900 per year compared to pre-January 2024 rates.
Income tax thresholds remain frozen at their 2021/22 levels — the personal allowance at £12,570, the basic rate limit at £50,270, and the higher rate limit at £125,140. This freeze, which is set to continue until 2027/28, means that as wages rise with inflation, more taxpayers are being pulled into higher tax bands — a process known as fiscal drag. The Office for Budget Responsibility estimates this will raise billions in additional tax revenue without any formal rate increases.
How Income Tax and NI Work Together
Income tax and National Insurance are calculated separately but both reduce your take-home pay. At a salary of £35,000, you would pay approximately £4,486 in income tax and £1,826 in National Insurance — a combined deduction of £6,312, giving an effective combined rate of around 18%. At £50,000, the combined deduction rises to approximately £12,232 (24.5%), and at £60,000 it rises sharply to around £16,232 (27%) as the higher income tax rate kicks in above £50,270.
One important distinction: income tax and NI have different thresholds. Income tax starts at £12,570 (the personal allowance), while employee NI also starts at £12,570 (the Primary Threshold). Employer NI, however, starts at just £9,100 (the Secondary Threshold) — meaning your employer pays NI on a larger portion of your salary than you do.
Reducing Your Tax Bill Legally
There are several legitimate ways to reduce your UK tax bill. Pension contributions are the most powerful tool available to most people — contributing to a pension reduces your taxable income, saving 20% for basic rate taxpayers, 40% for higher rate taxpayers, and 45% for additional rate taxpayers. For those earning between £100,000 and £125,140, pension contributions can reduce income below the threshold where the personal allowance starts to be withdrawn, effectively saving 60p in tax for every £1 contributed.
Salary sacrifice arrangements — where you agree to a lower salary in exchange for benefits such as pension contributions, childcare vouchers, or electric vehicle leasing — can reduce both income tax and National Insurance. Marriage Allowance allows one partner to transfer £1,260 of their personal allowance to the other (saving up to £252 per year) if one partner earns below the personal allowance. ISA contributions do not reduce your current tax bill but shelter future investment growth and income from tax entirely.
Frequently Asked Questions
What is the difference between the tax year and the calendar year?
The UK tax year runs from 6 April to 5 April the following year — not from 1 January to 31 December. This unusual date originates from the switch from the Julian to the Gregorian calendar in 1752. The 2024/25 tax year runs from 6 April 2024 to 5 April 2025.
Do I need to complete a Self Assessment tax return?
You must file a Self Assessment return if you are self-employed with income over £1,000, a company director, earn over £100,000, have untaxed income over £2,500, or have capital gains to declare. HMRC will usually write to you if they believe you need to file. Employees whose tax is fully collected through PAYE generally do not need to file.
How do I check if I am paying the right amount of tax?
You can check your tax code, estimated tax bill, and NI record through your Personal Tax Account at gov.uk/personal-tax-account. If you believe your tax code is wrong, contact HMRC on 0300 200 3300. Common reasons for incorrect tax codes include starting a new job, having multiple jobs, or receiving untaxed income.
What is the Marriage Allowance and how do I claim it?
Marriage Allowance lets you transfer £1,260 of your personal allowance to your spouse or civil partner if you earn less than the personal allowance (£12,570) and they are a basic rate taxpayer. This saves up to £252 per year. You can apply online at gov.uk/marriage-allowance and claims can be backdated up to 4 years.