The Junior ISA allowance is £9,000 for 2025/26. But what could that actually become by age 18?
Key finding: Since 2011, global stock markets have returned 6.5% annually vs 1.53% for cash Junior ISAs. That's over 4x the returns.
Assuming you invest the full £9,000/year from birth until age 18:
| Annual Return | Total Contributed | Value at 18 | Growth |
|---|---|---|---|
| 2% (cash savings) | £162,000 | £195,000 | £33,000 |
| 5% (bonds/mixed) | £162,000 | £262,000 | £100,000 |
| 7% (historical average) | £162,000 | £323,000 | £161,000 |
| 10% (optimistic) | £162,000 | £450,000 | £288,000 |
Based on monthly contributions of £750. Figures are estimates only.
Since 2011:
That's a difference of 4x over the decade.
Starting at different ages changes everything:
| Start Age | Years Invested | At 18 (7% return) |
|---|---|---|
| 0 (birth) | 18 | £323,000 |
| 5 | 13 | £190,000 |
| 10 | 8 | £96,000 |
| 15 | 3 | £30,000 |
Starting at birth vs age 10 means over 3x more at 18.
Money invested early grows on itself. The first £9,000 grows for 18 years. The last £9,000 grows for just 1 year.
But the first £9,000 at 7% becomes £32,000. That's the magic of compound interest.
Even small amounts add up:
| Monthly | Annual | At 18 (7%) |
|---|---|---|
| £50 | £600 | £21,500 |
| £100 | £1,200 | £43,000 |
| £250 | £3,000 | £108,000 |
| £500 | £6,000 | £215,000 |
| £750 | £9,000 | £323,000 |
Yes, investments can go down. But over 18 years, the stock market has never lost money.
The longest UK stock market downturn was 3 years (1973-1975). But the market recovered and went on to new highs.
Time in the market beats timing the market.
For long-term investing, we recommend:
See our full comparison: Best Junior ISA Platforms 2026
FCA Regulatory Disclaimer: This article is for educational and informational purposes only and does not constitute financial advice. IMZA Invest is not authorised or regulated by the Financial Conduct Authority (FCA) to provide financial advice. Nothing on this page should be construed as a recommendation to buy or sell any financial product.
Investment returns are not guaranteed. The value of investments can fall as well as rise, and you may get back less than you invest. Past performance is not a reliable indicator of future results. Tax treatment depends on your individual circumstances and may be subject to change. Junior ISA rules are set by HMRC and are subject to annual review.
All figures shown are projections based on compound interest calculations and are provided for illustrative purposes only. Actual returns will differ. Always seek regulated financial advice before making investment decisions.
Calculation methodology: Projections use the standard future value of annuity formula: FV = PMT × [((1 + r/12)^(12×n) − 1) / (r/12)], where PMT is the monthly contribution, r is the annual interest rate, and n is the number of years. Monthly compounding is assumed.
Sources: Hargreaves Lansdown JISA information; Scottish Friendly Junior ISA research (MSCI World average annual return vs cash Junior ISA average 2011–2021). Return rates used in projections are historical averages and are not guaranteed.