Saving & Investing
See how your ISA allowance could grow tax-free.
Estimate the future value of a Cash ISA or Stocks & Shares ISA, see how much of the annual ISA allowance you use and understand how much remains available.
ISA Calculator
Model your annual ISA subscriptions and potential tax-free growth.
Your ISA projection will appear here.
Compare your ISA subscriptions with the estimated tax-free growth.
How your ISA could grow
Illustrative year-by-year projection using your chosen rate and contribution.
Try changing your annual contribution, assumed rate, ISA type or timeframe to see how the projection changes.
This calculator models Cash ISAs and Stocks & Shares ISAs, not Lifetime ISAs. It uses the current overall ISA allowance as the annual contribution cap throughout the projection; future allowances and product-specific limits can change. The Cash ISA example rate is illustrative, and Stocks & Shares ISA returns are not guaranteed and can be negative.
What determines how your ISA could grow?
The projected value is mainly shaped by how much is contributed, the growth or interest rate assumed and how long the money remains invested or saved.
Amount contributed
The more money held within the ISA, the larger the amount that can potentially earn interest or investment growth.
Growth or interest rate
The assumed rate affects how quickly the ISA balance could increase over time.
Time
A longer period gives interest or investment growth more opportunity to accumulate.
What the ISA wrapper changes
An ISA is a tax-efficient wrapper. It can hold eligible cash or investments, but it does not create the underlying return itself.
Money goes into an ISA
Eligible contributions are placed inside the ISA wrapper, subject to the applicable ISA rules and allowance.
It earns interest or investment growth
The underlying cash or investments determine how the value changes over time.
Growth remains inside the wrapper
Interest, gains or investment growth can accumulate within the ISA rather than becoming new contributions.
ISA tax treatment can affect what you retain
The wrapper can shelter eligible interest, income or gains from UK tax under the ISA rules.
An ISA does not create investment return or savings interest. It is a tax-efficient wrapper around eligible savings or investments.
Cash ISA and Stocks & Shares ISA are not the same thing
They can both sit inside the ISA system, but the underlying source of growth and the risks are different.
Cash ISA vs Stocks & Shares ISA →Cash ISA
Normally earns savings interest. The balance itself does not fluctuate with investment markets.
Stocks & Shares ISA
Can hold investments whose value can rise or fall, so future returns are uncertain.
The ISA wrapper
Both can receive ISA tax treatment, but the wrapper does not make their underlying growth mechanics or risks the same.
The ISA allowance limits what you can contribute
The ISA allowance applies to subscriptions made during a tax year. Growth already inside the ISA is separate from the amount you contribute.
The allowance applies to contributions
It limits how much can be subscribed to eligible ISAs during the relevant tax year under the rules in force at that time.
Growth is different from contributions
Interest or investment growth generated inside the ISA does not normally count as a new subscription to the ISA.
ISA rules can change
Allowance amounts and other ISA rules are regulatory data and should always be checked against the current tax-year rules.
The calculator should illustrate the effect of the inputs entered rather than hard-code an allowance as a permanent editorial assumption.
An ISA is tax-efficient, not automatically better
The ISA wrapper can change the tax treatment of eligible savings or investments, but it does not guarantee growth or make an underlying product suitable for everyone.
The wrapper does not guarantee growth
An ISA can hold cash or investments, but its tax treatment does not determine the interest rate or investment return.
Investment values can fall
Where investments are held inside an ISA, their value may rise or fall and future returns are uncertain.
The tax advantage depends on what would otherwise be taxable
The practical value of ISA tax treatment can differ depending on the underlying return and the tax rules that would otherwise apply.
Use the calculator as an illustration of ISA growth assumptions, not as a recommendation to use a particular ISA, provider or investment.
Explore your next question
Once you have modelled ISA growth, the next useful step is to understand the wrapper, the allowance, the main ISA types and the underlying growth itself.
Go deeper
These guides explain the ISA wrapper, contribution rules and the main ways cash and investments can be held inside an ISA.
What Is an ISA and How Does It Work?
Understand what an ISA is, what the wrapper changes and how it fits into saving and investing in the UK.
Read the guide →Common questions about ISAs
These answers cover common questions that arise after modelling growth inside an ISA.
What does the ISA Calculator calculate?
It illustrates how money held within an ISA could grow over time using the contribution, rate and timeframe assumptions entered into the calculator.
What is an ISA?
An ISA is a UK tax-efficient wrapper that can hold eligible cash or investments. The wrapper affects tax treatment; the underlying cash or investments determine the actual return.
Does an ISA guarantee tax-free growth?
ISA tax treatment can shelter eligible interest, income and gains under the rules in force, but it does not guarantee that the underlying savings or investments will grow.
Is a Cash ISA the same as a Stocks & Shares ISA?
No. A Cash ISA normally earns savings interest, while a Stocks & Shares ISA can hold investments whose value can rise or fall.
Does ISA growth count towards the ISA allowance?
Growth generated inside an ISA does not normally count as a new subscription. The allowance applies to the amount contributed under the applicable tax-year rules.
Can I have more than one ISA?
It may be possible to hold more than one ISA, subject to the ISA rules in force. The dedicated ISA rules guides should be used for current detail.
What happens if I exceed the ISA allowance?
Exceeding the applicable subscription limit can create an ISA rules issue. The dedicated guide explains the current process and what to do next.
Can investments inside an ISA fall in value?
Yes. Investments held inside an ISA can rise or fall in value. ISA tax treatment does not remove investment risk.
What happens to an ISA at the end of the tax year?
Existing ISA holdings do not simply disappear at year end. Contribution rules operate by tax year, while money already held in an ISA can remain within the wrapper subject to the rules.
Is the ISA Calculator financial advice?
No. It is an educational illustration based on the assumptions entered and does not recommend a particular ISA, provider, investment or course of action.