ISA Savings & Tax calculator

Use this tool to forecast how much money you could save by putting money aside every month, and how much interest you could earn along the way. We’ll also show you how much you could be saving in UK tax by using an Individual Savings Account (ISA), whether it's a Cash ISA or Stock & Shares ISA. Lightyear does not offer ISAs.

How to use the ISA savings calculator

The UK government offers Individual Savings Accounts (ISAs) to eligible UK residents, to allow them to cut down the amount of tax that applies when saving and investing. There are several different types of ISA available, each with its own features and benefits - but what could an ISA really be worth to you? Use our smart and simple ISA calculator to find out.
This guide is intended for information use only. The value of any investment can go down as well as up - law, government policy and ISA options may also change over time. Consider all your options when it comes to saving and investing, based on your own personal risk appetite and timescales - get professional advice if you need it to make sure your investments work optimally for you.
Our ISA savings calculator shows you how much your ISA could be worth based on different rates of saving and different return rates, and also how much tax you can save by choosing to use an ISA instead of an alternative investment vehicle. We’ll talk a bit more about different types of UK ISA, who’s eligible and how they work - but first, a quick look at how to use the ISA calculator to get your personal projection.
To use our ISA calculator:
  1. Enter your deposit amount in pounds
  2. Enter the amount you’ll add as a regular monthly contribution
  3. Enter how long you want to run the calculation for (number of years of saving)
  4. Enter the ISA type (Cash ISA or Stocks & Shares ISA)
You’ll see the value of your investment over time based on the selected growth rate. And to see why it’s worth using an ISA if you’re a UK tax resident saving or investing, we can also show you an estimate of the tax savings you make thanks to the ISA wrapper, split out as a separate sum. For this, simply enter your annual income and we’ll do the rest.

What is an ISA? Individual Savings Accounts explained

ISA stands for Individual Savings Account. An ISA is known as a "tax wrapper" - that is an investment vehicle which can be used to protect some or all of your investment from taxation, subject to meeting government conditions.
There are 4 different types of ISA in the UK:
  • Cash ISA 
  • Stocks & Shares ISA
  • Innovative Finance ISA
  • Lifetime ISA
You can choose to pay into one of each of these ISA types in any given UK tax year, as long as you’re eligible. You’ve got an annual allowance which you can choose to use across different ISA types, or you may be able to put all your allowance that year into one specific ISA instead.
The annual allowance changes from time to time, but is 20,000 GBP in total in 2024. Of your annual allowance you can choose to add up to 4,000 GBP to a Lifetime ISA. Lifetime ISAs are a little more limited compared to the other ISA types, because you may benefit from a government bonus of up to 25% of your contribution. This ISA is intended for buying a home or for retirement, for example.
There are also Junior ISAs which can be opened by an adult in the UK, on behalf of a child under 18.

Who is eligible to open an ISA in the UK?

Your eligibility to open an ISA depends on your age, and your tax residency. You must be
  • 16 or over to open a Cash ISA
  • 18 or over to open a Stocks & Shares or Innovative Finance ISA
  • Between 18 and 40 to open a Lifetime ISA - you can pay into a Lifetime ISA annually until you’re 50 years old as long as you start contributing before you turn 40
In most cases you must be a resident of the UK - the key exception being if you’re considered to be a Crown servant or their spouse or civil partner. This exception means that people who work for the diplomatic services or overseas civil service may be able to open an ISA even if they’re not a UK resident.
If you open an ISA and then move abroad you’ll usually be able to keep your ISA open, but you can not add more money to it. Any savings and investments in your ISA when you leave the UK still receive tax relief in the same way that they did when you were resident. Check the UK government guidance on ISAs for more information.

Cash ISA vs Stocks & Shares ISA

The most common choices for ISAs tend to be Cash ISAs and Stocks & Shares ISAs - but what’s the difference?
Both Cash ISAs and Stocks & Shares ISAs can be issued by different banks, building societies and similar financial service providers, but how they’re made up does vary.
Cash ISAs can include:
  • Money saved in bank and building society accounts
  • Some National Savings and Investments (NS&I) products
While Stocks & Shares ISAs can include different assets like:
  • Shares in publicly floated companies
  • Unit trusts and investment funds
  • Corporate and government bonds
Because of the way these different ISA products are made up, their performance, risk and opportunity may vary significantly. You should take time to understand your options before you choose the right ISA type for your needs. Getting professional advice can help you to make sure you’re picking assets and saving options which are suited to your unique personal situation.

How much can you put into an ISA per year? 

There’s an annual ISA limit which is reviewed from time to time, and which can come with other stipulations and rules.
Different ISA providers may also offer varying products. For example, some ISAs are considered flexible which means you can take out money and then put it back in the same tax year without reducing your annual allowance amount. However, not all ISAs have this option.

What are the tax advantages of using an ISA?

You won’t have to pay tax on interest earned from a Cash ISA, or from income or capital gains amassed in a Stocks & Shares ISA. If you complete a tax self assessment for HMRC you don’t need to include any earnings from your ISA.
Depending on the amount you save or invest in an ISA, how long you leave it for, and what your own tax rate is, this can mean you cut down your overall tax. Our ISA investment calculator will split out the amount of tax saved as part of the calculation, as well as showing what your asset might be worth according to a variable model. We’ll look at the specific potential tax savings, and a few common questions, below.

Does my UK tax bracket matter to the amount of tax I can save with an ISA?

UK tax on savings interest can vary depending on your personal income tax bracket among other things. As you won’t pay tax on interest earned from savings held in an ISA, the amount of money you can save will also vary based on your normal tax bracket.
Generally UK tax residents can earn some interest on their savings before tax kicks in. The allowances which may apply are:
  • Your tax free personal allowance
  • The starting rate for savings
  • Your personal savings allowance
If your tax free personal allowance has not already been accounted for, this can be used to cover some interest on savings.
Once this has been used up, you may be entitled to an allowance of up to 5,000 GBP if your annual income from other sources is 15,570 GBP or under. If you earn under this amount, your savings allowance is offered on a sliding scale based on your income.
Finally, if you pay tax on your income at the basic rate in the UK you can also get another 1,000 GBP personal savings allowance - reduced to 500 GBP for higher rate taxpayers.
Sounds complicated? Don’t worry - all of these calculations have been built into our ISA calculator so you don’t need to do the maths. Just enter the required data into the calculator - including your annual income - then hit the 'Tax Savings' tab to see your projected savings.

What is the ISA tax free allowance?

Tax is subject to personal circumstances, but in general, if you have a Cash ISA you won’t pay tax on any interest you earn on it. The amount of money you can pay into your ISA annually is capped at 20,000 GBP a year at the time of writing.
If you’re saving in an account that is not covered by an ISA, and you use up the allowances we explored above, you pay interest on the remaining amount at your normal income tax rate. Generally that’s 20% for basic rate taxpayers, 40% for higher rate, and 45% for additional rate taxpayers. As you can see, the amount of money you can save on tax by making sure you use an ISA effectively every tax year is pretty significant!

What about capital gains tax (CGT) on an ISA?

You don’t pay tax on income or capital gains if you have a Stocks and Shares ISA.
Capital Gains Tax (CGT) is usually payable on the amount an asset increases in value from the point you buy or invest in it. CGT is payable at the point you sell the asset. Again, remember that tax is subject to personal circumstances.
As with interest, Capital Gains Tax is subject to annual allowances before any tax kicks in. For the 2024 tax year, that means you can gain by up to 3,000 GBP before being charged CGT. If you’re a basic rate taxpayer your CGT is likely to be 10% - 18% depending on the asset type involved. Higher and additional rate taxpayers pay 20% - 28% in CGT depending on the asset. Again - the savings to be had here by making good use of an ISA can be pretty staggering.

ISA savings calculator: Conclusion and summary

If you’re an eligible UK tax resident using an ISA to save or invest can help you pay less tax overall. Different ISA types are offered by many UK banks, building societies and other financial institutions. Use this ISA savings calculator to figure out what you might be able to achieve by making use of an ISA, including tax savings and underlying growth.