Read in other languages (18)
Summary
A Junior ISA (JISA) is a tax-free savings or investment account for children under 18 in the UK. Parents, grandparents, or anyone else can contribute up to £9,000 per tax year (2025/26). All growth — interest, dividends, and capital gains — is completely tax-free. At 18 the account automatically converts to an adult ISA and the money belongs to the child.
How it works
A child can hold up to two Junior ISAs: one Cash JISA (earns interest) and one Stocks & Shares JISA (invested in funds/shares). The combined annual contribution limit across both is £9,000.
Key rules:
- Only a parent or guardian with parental responsibility can open the account (for children under 16)
- Children aged 16–17 can open their own Junior ISA
- Anyone can contribute — parents, grandparents, family friends
- Money is locked until the child turns 18 (no withdrawals except terminal illness)
- At age 16, the child can become the registered contact and manage the account
- At age 18, the JISA automatically converts to an adult ISA
- Unused allowance cannot be carried over between tax years
- A child cannot hold both a Junior ISA and a Child Trust Fund
The formula
The calculator projects growth using annual compounding with end-of-year contributions — a conservative model since it assumes money is added at the end of each year rather than throughout.
Where
Equivalently, for a pure annuity (no initial deposit, no fees):
Where
Worked example
£100/month from birth at 5% return, no fees
Annual contribution
= £1,200
Years to maturity
= 18
Future value (annuity formula)
= £33,759
Total contributed
= £21,600
Investment growth
= £12,159
Result
Your child receives £33,759 at 18 — and £12,159 of that is free growth
The annual allowance
| Tax year | Annual limit |
|---|---|
| 2025/26 | £9,000 |
| 2024/25 | £9,000 |
| 2023/24 | £9,000 |
| 2022/23 | £9,000 |
| 2020/21 onwards | £9,000 (raised from £4,368) |
The £9,000 limit is shared across Cash and Stocks & Shares JISAs. For example, if you put £3,000 into a Cash JISA, you can contribute up to £6,000 to a Stocks & Shares JISA in the same tax year.
Inputs explained
- Child’s age — current age (0–17). Determines the number of years until the JISA matures at 18.
- Initial deposit — a lump sum to start with (up to £9,000, the annual limit).
- Monthly contribution — regular monthly amount. The calculator annualises this and caps at the £9,000/year allowance.
- Expected annual return — the assumed annual growth rate. Typical assumptions: 2% (cash), 5% (conservative equity), 7% (historic stock market average).
- Annual fees — platform and fund management fees, deducted from growth. Typical range: 0.15% (Vanguard LifeStrategy via iWeb) to 1.5% (actively managed funds on legacy platforms).
Outputs explained
- Value at 18 — projected JISA balance when the child turns 18
- Total contributed — sum of initial deposit plus all annual contributions
- Investment growth — total growth earned on the balance (gross, before fee deduction)
- Fees paid — total fees deducted over the investment period
- Growth multiple — how many times your contributions have multiplied (e.g., 1.56× means 56% growth)
- Daily equivalent — monthly contribution expressed as a daily amount, to make it feel more tangible
Assumptions & limitations
- Annual compounding — growth is calculated once per year. Real investments fluctuate daily, but annual compounding is standard for long-term projections and is slightly conservative.
- End-of-year contributions — contributions are modelled as being added at the end of each year. Real monthly contributions would produce slightly higher returns due to intra-year compounding.
- Constant return rate — a fixed annual return is assumed. In reality, stock market returns vary significantly year to year. The projection shows an average-case scenario.
- Constant fee rate — fees are assumed to be a fixed percentage of the balance. Some providers charge flat fees (e.g., £9.99/month) which would affect smaller pots more.
- No inflation adjustment — the projected value is in nominal terms. To estimate real (inflation-adjusted) purchasing power, subtract 2–3% from the expected return.
- Allowance assumed constant — the £9,000 limit is assumed to remain unchanged. HMRC may adjust it in future budgets.
What happens at 18
When the child turns 18:
- The Junior ISA automatically converts to an adult ISA
- The money belongs to the child — they have full control
- They can keep it invested, transfer to a different provider, or withdraw
- All growth remains tax-free within the ISA wrapper
- The converted amount does not count towards their adult ISA allowance for that year
Verification
| Test case | Input | Expected value at 18 | Our result | Source |
|---|---|---|---|---|
| Basic monthly saving | £100/m, age 0, 5%, 0% fees | £33,759 | £33,759 | Annuity formula |
| With fees | £100/m, age 0, 5%, 1.5% fees | £29,400 | £29,400 | Manual calculation (net rate 3.5%) |
| Lump sum + monthly | £5k + £200/m, age 5, 6%, 0.75% fees | £52,918 | £52,918 | Lump sum FV + annuity FV |
Sources
Related calculators
ISA
Calculate how much your ISA could be worth tax-free. Compare Cash ISA, Stocks & Shares ISA, and Lifetime ISA with 25% government bonus. See how much tax you save vs a regular account.
Compound Interest
Project how your savings or investments grow over time with compound interest. See contributions vs growth with a chart.
Investment Fees
Calculate how much investment fees cost you over time. Compare low-cost index funds vs actively managed funds and see the compound impact of fees on your ISA, pension, or investment portfolio.