How can an ISA save you over £90000 in Tax?
The Individual Savings Account is one of the most powerful tax-saving tools available to UK taxpayers. Many people know ISAs are “tax-free” but few understand just how much money this saves. This article shows you exactly how maximising your ISA allowance could save you over £90,000 in tax over 15 years although no return is guaranteed. Please note this is for demonstration purposes only and does not resemble any real cases, but highlights the advantages of long term ISA savings.
What Is An ISA?
An Individual Savings Account (ISA) is a tax-free wrapper for your savings and investments. Think of it as a protective shield around your money that stops HMRC taking tax from your returns.
The key benefits are simple:
- No tax on interest from cash savings
- No tax on dividends from investments
- No tax on investment growth
- No tax when you withdraw money
Your ISA Allowance For 2025/26
Every UK resident aged 18 or over can put up to £20,000 into ISAs each tax year. This allowance resets on 6th April and you cannot carry forward unused amounts. If you don’t use it, you lose it forever.
There are many different types of ISA including:
Cash ISAs – Savings accounts with tax-free interest. Good for short-term goals and emergency funds.
Stocks and Shares ISAs – Investments in funds and shares with tax-free growth. Better for long-term goals over five years.
Lifetime ISAs – For first-time buyers or retirement (ages 18-39). Government adds 25% bonus but charges penalties for other withdrawals.
Kowing which one that is right for you depends on what you are saving for and the time horizon for your savings.
What Tax Would You Pay Without An ISA?
To understand ISA savings, you need to know what tax you would pay on savings and investments outside an ISA. This is communicated in the Budget each year.
On Savings Interest
You get a Personal Savings Allowance:
- Basic rate taxpayers: £1,000 tax-free
- Higher rate taxpayers: £500 tax-free
- Additional rate taxpayers: £0 tax-free
Interest above these amounts is taxed at 20%, 40% or 45% depending on your income.
On Investment Dividends
You get a £500 Dividend Allowance in 2025/26. Dividends above this are taxed at:
- 8.75% for basic rate taxpayers
- 33.75% for higher rate taxpayers
- 39.35% for additional rate taxpayers
On Investment Growth
You get a £3,000 Capital Gains Tax allowance. Gains above this are taxed at:
- 18% for basic rate taxpayers
- 24% for higher rate taxpayers
These various taxes should be reported on your self assessment tax return.
ISAs eliminate all these taxes completely.
How can an ISA save you over £90000 in Tax?
Please note this is an extreme example of a specific set of circumstances and it is for demonstration purposes only.
Our client, Michael is 45 years old, earns £65,000 and pays 40% higher rate tax. He wants to invest £20,000 per year for 15 years until he turns 60 in an adventurous risk.
The Setup
- Invests: £20,000 per year for 15 years
- Total contributions: £300,000
- Investment return: 8% per year average (Investment returns are never guaranteed, investment can go down as well as up and you may get back less than invested)
- Estimated Final value after 15 years: £544,000
Now let’s compare what happens with and without an ISA.
Option 1: Investing WITHOUT An ISA
Michael invests his £20,000 each year in a standard investment account.
The Tax Bills
Each year his investments generate estimated dividends (around 2% of the value). As his portfolio grows, so does his tax bill:
- Year 5: Portfolio worth £117,000, dividend tax £621
- Year 10: Portfolio worth £290,000, dividend tax £1,789
- Year 15: Portfolio worth £544,000, dividend tax £3,503
Total dividend tax over 15 years: £22,500
When Michael sells his investments to access the money, he faces Capital Gains Tax:
- Total value: £544,000
- What he paid in: £300,000
- His gain: £244,000
- Tax-free allowance: £3,000
- Taxable gain: £241,000
- Tax at 24%: £57,840
Total tax paid: £93,200
Money Michael keeps: £450,800
Option 2: Investing WITH A Stocks And Shares ISA
Michael invests the same £20,000 each year into a Stocks and Shares ISA. Same investments, same returns, same final value of £544,000.
The Tax Bills
- Dividend tax: £0
- Capital Gains Tax: £0
- Withdrawal tax: £0
Total tax paid: £0
Money Michael keeps: £544,000
The Simple Comparison
Without ISA:
- You contribute: £300,000
- It grows to: £544,000
- You pay tax: £93,200
- You keep: £450,800
With ISA:
- You contribute: £300,000
- You pay tax: £0
- You keep: £544,000
The difference: £93,200 in your pocket instead of HMRC’s
That is real money. It could help pay for a comfortable retirement, help your children buy their first home or give you financial security and peace of mind or better still fund your bucket list.
Why ISAs Save You More Over Time
The longer you use ISAs, the more valuable they become:
Year 1 – Small portfolio, small tax saving Year 5 – Growing portfolio, tax savings increasing
Year 10 – Large portfolio, substantial annual tax savings
Year 15 – Very large portfolio, huge tax savings
In Michael’s example, by year 15 he was avoiding over £3,500 in dividend tax in that single year alone, plus the entire £57,840 capital gains tax bill.
If Michael continued to age 75 (30 years total), his ISA would be worth approximately £1,486,000 and the tax savings would exceed £200,000.
Five Simple Actions To Maximise Your ISA Savings
- Use Your Full £20,000 Allowance Each Year
The allowance doesn’t roll over. If you only use £10,000 this year, you cannot make up the difference next year. Each 6th April you get a fresh £20,000 regardless of what you used before.
- Start As Early As Possible
Time is your best friend. If Michael had started at 35 instead of 45, his tax savings would exceed £175,000 instead of exceeding £90,000.
- Choose The Right ISA Type
Cash ISAs for short-term goals and emergency funds. Stocks and Shares ISAs for long-term goals beyond five years where you can accept investment risk for potentially higher returns.
- Invest Early In The Tax Year
Contributing on 6th April instead of 5th April the following year gives your money an extra year to grow tax-free. Over 15 years this adds thousands of pounds.
- Transfer, Don’t Withdraw
Moving between ISA providers? Use the formal transfer process. If you withdraw and recontribute, you use up your current year’s allowance, so have wasted your diligent savings.
Quick Answers To Common ISA Questions
Can I access my ISA money?
Yes. Cash ISAs and Stocks and Shares ISAs let you access money anytime without penalty. Some fixed-rate Cash ISAs lock your money for higher interest. Lifetime ISAs charge 25% penalties for non-property/retirement withdrawals.
Do I declare ISAs on my tax return?
No. ISAs are not taxable so they don’t go on Self Assessment returns.
What happens to my ISA when I die?
Your spouse or civil partner gets a one-time additional ISA allowance equal to your ISA value, preserving the tax benefits.
Are ISAs protected?
Yes. The Financial Services Compensation Scheme protects your money per person per institution if your provider fails. Check website for latest allowances. Bank & savings protection checker | Check your money is protected | FSCS
Why Professional Advice Makes A Difference to your ISA strategy
ISAs are simple in principle but getting the most from them requires careful planning:
- Which ISA type suits your specific goals
- Should you prioritise ISAs or pensions given your tax position
- How to invest your ISA money based on your risk tolerance
- How ISAs fit with inheritance tax planning
- Whether Lifetime ISAs suit your circumstances
A qualified financial planner can model your situation and show you exactly how much tax different strategies would save you. The cost of advice is typically far less than the additional tax savings identified.
Take Action Now
The £93,200 saving in this example is the money you can keep instead of paying to HMRC. But it only happens through action.
Every tax year without maximising your ISA allowance is lost tax relief you can never recover.
Your 2025/26 allowance expires 5th April 2026.
If you haven’t used your £20,000 allowance yet, you have until 5th April to contribute. If you have used it, start planning now for your 2026/27 allowance from 6th April onwards.
The mathematics proves ISAs save substantial tax. The only question is whether you will take action to claim these savings for yourself and your family.
This is just one in an array of financial planning strategies that a financial planner can use, to legitimately minimise the tax you pay. Always seek professional advice to ensure this is the correct strategy for you.
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BE AWARE
This information is for guidance only and does not constitute regulated financial advice. To ensure you have personalised advice for your particular set of circumstances, you must make an appointment and speak to one of our professional advisers. Please note these services are chargeable. The facts in this article were correct at time of writing, but you may be reading it in the future. Always check rates and allowances before taking action or speak to a qualified financial planner. All investments carry an element of risk, they can fall as well as rise and you may not get back what you pay in. Errors & omissions excepted.
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