Project tax-free growth for Cash ISA or Stocks and Shares ISA — with allowance tracker and yearly breakdown.
Calculate Your ISA Growth
Risk warning: Stocks and Shares ISAs invest in financial markets. The value of your investment can go down as well as up, and you may get back less than you put in. The growth rate you enter is an assumption only — past performance is not a reliable indicator of future returns. This calculator is for illustrative purposes and is not financial advice.
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Leave at 0 if starting from scratch
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Regular amount you will add each month
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Use the AER shown on your Cash ISA
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Annual ISA contribution rate£0 / £20,000 allowance
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Final ISA Balance
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Growth Earned
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Total Contributed
ISA type
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Initial deposit
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Monthly contributions
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Total contributed
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Annual interest rate (AER)
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Investment period
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Total growth earned
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Tax-free wrapper: All interest, growth and dividends inside an ISA are completely free of Income Tax and Capital Gains Tax — no need to declare them on a self-assessment return. The annual allowance is £20,000 per person per tax year (2026/27). Unused allowance does not carry forward.
Looking ahead: This calculator uses the current 2026/27 rules, which continue until 5 April 2027. From 6 April 2027 the overall £20,000 allowance is unchanged, but a £12,000 Cash ISA sub-limit applies to people under 65 (people aged 65+ keep the full £20,000 in cash). See ISA Reform from 6 April 2027 below.
Year
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Growth
Cumulative Growth
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How the ISA Calculator Works
This calculator projects how money grows inside an Individual Savings Account (ISA) using compound interest. The same mathematical formula applies to both Cash ISAs (interest) and Stocks and Shares ISAs (investment growth) — the difference is tax treatment and risk level, not the underlying projection method.
The Growth Formula
The calculator uses the standard compound interest formula with monthly compounding:
Where P is the initial deposit, r is the annual rate, t is years, and PMT is the monthly contribution. Contributions are treated as end-of-period payments. For Stocks and Shares ISAs, the rate represents an assumed annual growth rate — not a guaranteed return.
ISA Types at a Glance
ISA type
Tax treatment
2026/27 limit
Risk
Best for
Cash ISA
Tax-free interest
£20,000*
Low
Short–medium term goals
Stocks & Shares ISA
Tax-free growth & dividends
£20,000*
Medium–high
Long-term wealth building (5+ yrs)
Lifetime ISA (LISA)
Tax-free + 25% bonus
£4,000 (sub-limit)
Low–high
First home or retirement
Junior ISA
Tax-free
£9,000
Low–high
Children's savings (under 18)
Innovative Finance ISA
Tax-free interest
£20,000*
High
Peer-to-peer lending
* Total contributions across all ISA types cannot exceed £20,000 per tax year.
ISA Allowance Rules (2026/27)
The annual ISA allowance is £20,000 per person, running from 6 April 2026 to 5 April 2027. Key rules to know:
You can split the £20,000 across as many ISA types as you like
Since April 2024, you can contribute to multiple ISAs of the same type (e.g. two Cash ISAs) in the same tax year
Unused allowance is lost at the end of each tax year — it cannot be carried forward
Married couples and civil partners each have their own £20,000 allowance (£40,000 combined)
Withdrawals from a flexible ISA can be replaced in the same tax year without using additional allowance
Cash ISA vs Stocks and Shares ISA
Cash ISA: Works like a standard savings account but sheltered from tax. Interest rates track the Bank of England base rate and are typically lower than investment returns over the long term. Suitable for emergency funds, short-term goals, or anyone who cannot tolerate investment risk. Current best rates in 2026 range from 4–5% AER.
Stocks and Shares ISA: Invests in the stock market, funds, bonds and investment trusts. Returns are variable — the market value rises and falls. The UK and global stock markets have historically returned around 7–8% per year on average over the long term (including reinvested dividends), but this is not guaranteed and individual years can show significant losses. Generally only suitable if you can commit funds for at least 5 years.
The Lifetime ISA
The Lifetime ISA (LISA) is a powerful option for eligible savers. You must be aged 18–39 to open one. You can contribute up to £4,000 per year and receive a 25% government bonus added automatically — up to £1,000 free money per year. The LISA allowance counts within your £20,000 overall ISA limit. Funds can only be used to purchase a first home (worth up to £450,000) or from age 60. Withdrawing early incurs a 25% HMRC withdrawal charge — this claws back the bonus and 6.25% of your own money.
Why Starting Early Transforms ISA Outcomes
Compound growth inside an ISA accelerates dramatically over time. £400/month in a Stocks and Shares ISA at 7% over 25 years produces roughly 5× more growth than over 10 years — not 2.5×. The ISA wrapper means none of that growth is eroded by tax, making it especially powerful for long-term wealth building. Maximising your allowance in early tax years delivers the greatest compounding benefit.
ISA Reform from 6 April 2027 — Confirmed Changes
On 23 June 2026 the government published its 2026 Tax Update and an ISA reform factsheet confirming a package of changes to adult ISAs. These changes take effect from 6 April 2027 and are subject to detailed regulations still to be laid. The current 2026/27 rules above remain unchanged until 5 April 2027 — this calculator continues to use those current rules.
What is not changing: the overall £20,000 adult ISA allowance, the Lifetime ISA rules (£4,000 limit, 25% bonus, £450,000 property cap, withdrawal penalty), and the £9,000 Junior ISA allowance. The Personal Savings Allowance is unchanged.
1. Cash ISA sub-limit by age
The overall £20,000 ISA allowance is unchanged. From 6 April 2027 it is split as follows:
Age
Maximum into a Cash ISA
Maximum into other ISA types
Overall allowance
Under 65
£12,000
Up to £8,000 (subject to LISA £4,000 sub-limit)
£20,000
65 or over
£20,000
Up to £20,000 instead of cash
£20,000
The higher £20,000 Cash ISA limit applies from the start of the tax year in which the person turns 65, not from the birthday itself. For example, someone turning 65 in November 2027 would have the £20,000 Cash ISA limit available for the whole of 2027/28.
The remainder of the £20,000 allowance can be subscribed to a Stocks and Shares ISA, a Lifetime ISA (still capped at £4,000), an Innovative Finance ISA, or any combination, subject to the existing rules for each product.
2. A 22% charge on cash-like returns inside non-Cash ISAs
From 6 April 2027 a flat 22% charge will apply to interest and alternative-finance returns paid on cash held within a Stocks and Shares ISA or an Innovative Finance ISA. Key points:
The charge applies to returns on cash-like assets only — not to dividends, capital gains or ordinary investment growth.
It is paid by the ISA manager to HMRC, not by individual investors.
The Personal Savings Allowance does not offset this charge.
Normal investment income from shares, ordinary investment funds, ETFs, investment trusts, corporate bonds, government bonds and UK gilts continues to be free of UK Income Tax and Capital Gains Tax inside a Stocks and Shares ISA — these assets are not treated as cash-like for this measure.
Money market funds may continue to be held in a Stocks and Shares ISA as part of a wider portfolio, but an account cannot consist entirely of money market funds.
3. Transfer rules from 6 April 2027
Under 65: transfers from a non-Cash ISA (for example a Stocks and Shares ISA) into a Cash ISA will generally not be permitted.
Aged 65 or over: this transfer restriction will not apply in the same way.
Transfers from a Cash ISA into a non-Cash ISA will remain possible for all ages.
Existing transfer mechanics within the same ISA type (for example Cash ISA to Cash ISA) are unaffected by the reform announcement.
4. Lifetime ISA, Junior ISA and Personal Savings Allowance
No changes to the Lifetime ISA, Junior ISA or Personal Savings Allowance have been confirmed as part of this package. The Lifetime ISA continues at £4,000/year with a 25% government bonus, a £450,000 property-price cap and the existing 25% withdrawal penalty. The Junior ISA allowance remains £9,000.
Status: these are confirmed measures taking effect from 6 April 2027, subject to detailed regulations still to be laid. UKCalc will update this calculator if any element changes during the regulation-making process.
First Time Buyer ISA — Proposed and Under Consultation
Alongside the 2027 reforms, the government launched a consultation on a new First Time Buyer ISA. This product is proposed and not yet available. Final rules will only be known once the consultation concludes and legislation is laid. Nothing on this page should be read as suggesting the First Time Buyer ISA is available now.
What is being proposed
It is intended to be offered, over time, instead of opening a new Lifetime ISA.
Minimum opening age of 18, with no upper age limit.
Both cash and stocks-and-shares versions are envisaged.
Funds may be used solely to purchase a first home, with the purchase made using a mortgage.
A government bonus would be paid at the point of an eligible home purchase, rather than when contributions are made.
No Lifetime ISA-style withdrawal penalty on funds taken back out.
A possible minimum 12-month holding period before the account can be used for purchase.
Interaction rules with the Lifetime ISA and the Help to Buy ISA are part of the consultation.
Existing Lifetime ISA holders are expected to be allowed to continue contributing under the existing Lifetime ISA rules indefinitely.
What is not yet confirmed
The bonus rate.
The annual contribution limit.
The property-price cap.
The launch date.
The final eligibility rules.
The final interaction rules with Lifetime ISAs and Help to Buy ISAs.
If you are saving for a first home today: the existing Lifetime ISA rules continue to apply for the whole of 2026/27 and beyond for current holders. There is no need to act on the First Time Buyer ISA proposals until detailed rules and a launch date are confirmed. See our Lifetime ISA guide and first-time buyer guide.
Sources
GOV.UK — Individual Savings Accounts (ISA) guidance for the 2026/27 tax year.
GOV.UK — ISA reform 2027 anti-circumvention rules factsheet (published 23 June 2026).
GOV.UK — Tax Update 2026 summary (published 23 June 2026).
GOV.UK — First Time Buyer ISA consultation (open consultation linked from the Tax Update 2026).
UKCalc reads each source directly rather than relying on press summaries. This page is for information only and is not financial advice — speak to a regulated adviser for advice on your circumstances.
Last reviewed: 27 June 2026.
Worked Examples
Three realistic UK ISA scenarios — projected with monthly compounding and end-of-period contributions.
Stocks and Shares ISA projections assume a fixed annual growth rate maintained throughout the period. Actual returns will fluctuate with market conditions. Cash ISA projections assume the stated interest rate is maintained — variable rates will change over time. Not financial advice.
Frequently Asked Questions
The ISA allowance for 2026/27 is £20,000 per person per tax year (6 April 2026 to 5 April 2027). This can be split across a Cash ISA, Stocks and Shares ISA, Innovative Finance ISA, and Lifetime ISA (capped at £4,000 within the £20,000 total). All interest, growth and dividends inside an ISA are completely free of Income Tax and Capital Gains Tax. Unused allowance is lost at the end of the tax year — it cannot be rolled over to the next year.
A Cash ISA earns tax-free interest on cash — it works like a standard savings account but the interest is always tax-free, regardless of how much you earn. A Stocks and Shares ISA invests in the stock market (funds, shares, bonds, investment trusts), with tax-free growth and dividends. Cash ISAs offer capital security but lower expected returns. S&S ISAs offer higher expected long-term returns but your capital is at risk. As a rule of thumb: use Cash ISA for money you may need within 5 years, and S&S ISA for longer-term goals where you can ride out short-term market falls.
A Lifetime ISA (LISA) is available to people aged 18–39. You can contribute up to £4,000 per tax year and the government adds a 25% bonus — up to £1,000 free per year. The £4,000 limit is a sub-limit within your overall £20,000 ISA allowance. LISA funds can only be used to buy a first home (worth up to £450,000) or accessed from age 60. Withdrawing for any other reason triggers a 25% HMRC penalty, which claws back the bonus and 6.25% of your own contributions. If you are saving for a first home or retirement, the LISA is one of the most generous government savings incentives available.
Yes — since April 2024 the rules changed to allow contributions to multiple ISAs of the same type in the same tax year. For example, you can hold two Cash ISAs with different providers and contribute to both in 2026/27. You can also hold a Cash ISA and a Stocks and Shares ISA simultaneously. The only constraint is that your total contributions across all ISAs must not exceed £20,000 in a single tax year. Each provider is responsible for tracking your contributions to them, and HMRC monitors compliance across providers.
From 6 April 2027 the overall adult ISA allowance remains £20,000. For people under 65, the amount that can be subscribed to a Cash ISA in a tax year becomes £12,000, with the remaining £8,000 of the £20,000 allowance available for other eligible ISA types. For people aged 65 or over the Cash ISA limit remains £20,000, and the higher limit applies from the start of the tax year in which the person turns 65. A flat 22% charge will apply to interest and alternative-finance returns paid on cash held within Stocks and Shares ISAs and Innovative Finance ISAs — this is paid by the ISA manager to HMRC, is not offset by the Personal Savings Allowance, and does not turn normal investment growth, dividends or capital gains into taxable income. Under-65s will generally be unable to transfer from a non-Cash ISA into a Cash ISA, while transfers from a Cash ISA into a non-Cash ISA will remain possible. These changes are subject to detailed regulations still to be laid; current 2026/27 rules continue unchanged until 5 April 2027.
The First Time Buyer ISA is a proposed new product on which the government is consulting, intended over time to be offered instead of opening a new Lifetime ISA. Current proposals include a minimum opening age of 18 with no upper age limit, cash and stocks-and-shares versions, use solely for purchasing a first home with a mortgage, a government bonus paid at the point of an eligible home purchase rather than on each contribution, no Lifetime ISA-style withdrawal penalty, and a possible minimum 12-month holding period. Existing Lifetime ISA holders are expected to be allowed to continue contributing under the current rules. The bonus rate, annual contribution limit, property-price cap, launch date, final eligibility and final interaction rules with Lifetime ISAs and Help to Buy ISAs have not been confirmed. UKCalc will update this page once detailed rules are confirmed.