Free to use – No personal details required – 2025 UK Data
ISA Growth Calculator
Created by Dan Franks
Last Updated: 21st August 2025
Quick and easy
ISA growth calculator
Work out the estimated future value of your ISA by entering your initial investment, monthly contributions, growth rate, and term, with results showing total contributions, growth earned, and projected value over time.
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Results
Total Future Value: £0.00
Total Contributions: £0.00
Total Growth Earned: £0.00
| Year | Start Balance | Contribution | Growth | End Balance |
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Disclaimer: This calculator provides an estimated projection of potential investment growth. Actual returns may vary due to market performance, and are also influenced by various fees and charges from providers, which are not included in this calculation. This projection does not account for taxes or inflation.
For personalised financial advice, please consult a qualified financial adviser.
Why use our ISA growth calculator?
It can be hard to picture how savings build inside an ISA, especially when growth compounds over many years. Our calculator helps by giving you a clear estimate of how your ISA could grow, showing not just the final total but also how your balance changes year by year.
You can see the effect of starting with a lump sum, adding monthly contributions, or changing the growth rate and investment term. Results update instantly, so you can try out different scenarios and immediately see how small changes can alter your future balance.
The calculator displays your projected total value, how much of that comes from your own contributions, and how much is growth. You can switch between chart and table views for a breakdown that suits you best.
The benefit is clarity. Instead of relying on rough guesses, you get a straightforward estimate of what your ISA could be worth over time, helping you understand the potential impact of saving and investing through an ISA.
Our guarantees to you!
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We don’t collect or store any personal information.
Understanding Individual Savings Accounts (ISAs)
An Individual Savings Account (ISA) is a tax-efficient way to save or invest. All returns are exempt from tax, whether they come from income, capital gains or dividends.
Types of ISAs
There are five primary types of Individual Savings Accounts, each with distinct rules, contribution limits, and asset classes.
Cash ISA
A Cash ISA is a savings account that pays interest free from tax. It can be structured as an instant access, notice, or fixed-term account.
Capital protection, risks, and suitability
Your capital is protected by the Financial Services Compensation Scheme (FSCS) up to £85,000 per person, per provider. However, these ISAs are susceptible to inflation risk if interest rates are lower than inflation.
Cash ISAs are best for short- to medium-term savings goals where capital security is paramount, such as emergency funds.
Stocks and Shares ISA
A Stocks and Shares ISA allows you to hold company shares, corporate and government bonds, OEICs, unit trusts, investment trusts, and ETFs. All capital gains, dividends, and interest are tax-exempt.
Investment horizon, volatility, and management
This ISA is suited for long-term investing (typically five years or more) where investors accept potential short-term volatility for higher long-term returns. Losses are possible, and growth is not guaranteed.
FSCS protection applies to uninvested cash and, in limited cases, to assets with failed custodians, but not to investment performance. Commonly used for retirement savings, long-term wealth building, or funding future costs like university fees.
Innovative Finance ISA (IFISA)
The IFISA allows individuals to earn tax-free interest by lending money through FCA-authorised peer-to-peer (P2P) lending platforms or investing in debt-based securities.
Risks, protection, and liquidity
There is no FSCS protection, meaning partial or total loss of capital is possible if borrowers default or platforms fail. Some platforms offer contingency funds, but these are not guaranteed.
Liquidity can be limited, as early access to funds may be restricted or subject to discounts unless a secondary market is available. Suitable for investors seeking potentially higher returns than Cash ISAs who are willing to accept credit risk and reduced liquidity.
Lifetime ISA (LISA)
The LISA is designed for saving for a first home or retirement, boosted by a government bonus. LISAs can hold either cash or investments.
Eligibility, contributions, and withdrawals
Only individuals aged 18 to 39 can open a LISA, with contributions allowed up to age 50. You can contribute up to £4,000 annually, which counts towards your overall ISA allowance. For every £4 contributed, the government adds a £1 bonus, up to a maximum of £1,000 per tax year.
Funds can be withdrawn tax-free for a first home purchase (up to £450,000 property value) or from age 60 for any purpose. Withdrawals for other reasons incur a 25% penalty, which reduces both the bonus and a portion of your original contribution.
Most effective for those with a clear goal of buying a first home or supplementing pension savings long-term.
Junior ISA (JISA)
A Junior ISA is a long-term, tax-free savings or investment account for children under 18. A parent or legal guardian opens and manages the account, but the funds legally belong to the child and are locked until their 18th birthday.
The annual subscription limit is £9,000 for the 2025/2026 tax year, applying per child regardless of who contributes. Cash JISAs offer tax-free interest and principal protection, while Stocks and Shares JISAs provide tax-free growth on investments.
Upon turning 18, the JISA automatically converts into an adult ISA, giving the child full control and access to the funds.
How ISAs Work in Practice
Opening an ISA
To open an ISA, you must meet specific eligibility criteria. For most adult ISAs, you must be 18 or over (16 for a Cash ISA). The process involves choosing a provider, selecting the ISA type, providing proof of identity and UK residency, and completing an application.
Contributing money
Only the ISA holder can contribute, using their own money. Contributions count towards the annual ISA allowance, which is £20,000 for 2025/2026. This total can be split across multiple ISAs, including multiple of the same type, provided the aggregate amount does not exceed the allowance.
What happens inside the isa
Once funds are within an ISA, they are shielded from tax. Interest, dividends, and capital gains all grow tax-free. Investments can be traded within an ISA without triggering capital gains or income tax.
Managing the ISA
You can make additional contributions (within limits), switch investments, or transfer accounts between providers while preserving tax-free status. Funds from previous tax years can be transferred without affecting the current year’s allowance. However, current-year subscriptions must be transferred in full.
Withdrawing funds
Withdrawals from most ISA types are tax-free. Some ISAs are “flexible,” allowing withdrawn amounts to be replaced within the same tax year without affecting the annual allowance. Non-flexible ISAs do not offer this.
Isa tax treatment and allowance
All interest, capital gains, and dividends within an ISA are entirely tax-free. This exemption applies throughout the holding period and upon withdrawal.
Each tax year (April 6th to April 5th), individuals can contribute up to £20,000 across all ISA types (2025/2026 allowance). This allowance does not roll over; any unused portion is lost at the end of the tax year.
Illustrative examples
Here are two examples to illustrate how ISAs function in different situations:
Stocks and Shares ISA Example
In April 2025, James, a basic rate taxpayer, invests £10,000 into a Stocks and Shares ISA. Over the course of the 2025/26 tax year, his holdings generate £250 in dividend income and increase in value by £250. His total return for the year is £500.
Because the investment is held within an ISA, James pays no income tax on the dividend income and no capital gains tax on the £250 gain. He keeps the full £500.
In a general investment account, the £250 dividend income would fall within the £500 dividend allowance for 2025/26. If James had no other dividends, no tax would be due. If the allowance had already been used, the £250 would be taxed at 8.75%, resulting in a £21.88 charge.
The £250 capital gain would be assessed against the £3,000 annual CGT allowance. If the allowance had already been used, the gain would be taxed at 10%, producing a £25 charge.
If both allowances had been used, James would pay £46.88 in tax, reducing his net return to £453.12. By holding the investment in an ISA, he keeps the full amount.
Over time, as returns increase, all income and gains remain tax free inside the ISA.
Summary
James’s £10,000 Stocks and Shares ISA returned £500 tax-free. The same investment outside an ISA would have yielded only £453.12 after £46.88 in tax.
Cash ISA
In April 2025, Daniel, a higher rate taxpayer, deposits £15,000 into a one year fixed rate Cash ISA offering 4% annual interest. Over the course of the 2025/26 tax year:
- The account grows to £15,600.
- The £600 of interest earned is completely tax free.
Because the savings are held within a Cash ISA, Daniel pays no income tax on the interest. He keeps the full £600, and there is no requirement to report it to HMRC.
In contrast, the same £15,000 placed in a standard fixed rate savings account at 4% would also generate £600 interest. As a higher rate taxpayer, Daniel is not entitled to a Personal Savings Allowance. The full £600 would be taxed at 40%, resulting in a £240 tax charge.
His net return outside the ISA would be £360, reducing the effective interest rate from 4% to 2.4%.
By holding the savings in a Cash ISA, Daniel avoids the tax and retains the full return.
Over time, if the same deposit were made each year, the annual tax saving would repeat. The cumulative effect of keeping all interest earned would result in a significantly higher overall return.
Summary
Daniel saved £240 in tax by earning £600 interest completely tax-free in his Cash ISA, compared to only keeping £360 in a standard taxable account.
Key rules and restrictions
- Subscription Limits. £20,000 annual allowance across all ISA types. You can open multiple ISAs of the same type within a single tax year, provided the aggregate contributions do not exceed this total.
- Age Limits. Most adult ISAs require the holder to be 18 or over. Lifetime ISA contributions are specific to ages 18-39.
- Transfers. You can transfer existing ISA funds between different providers or ISA types without affecting the current year’s allowance. Current-year subscriptions must be transferred in full.
- Withdrawals. Most ISA withdrawals are tax-free. “Flexible ISAs” allow you to replace withdrawn funds within the same tax year without consuming new allowance.
- Residency. You must typically be a UK resident. Exceptions apply to Crown employees serving overseas and their spouses or civil partners.
Do you want more information on Individual Saving Accounts (ISA)?
Try these websites:
👉🏼 GovUK
👉🏽 Halifax
👉🏿 Money Saving Expert
Please note: We are not affiliated with, endorsed by, or responsible for the content of any third-party websites linked to from this site. Links open in a new tab.
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