Junior ISA Calculator UK 2026
Common JISA questions (from r/UKPersonalFinance)
Can I open a JISA for my child if grandparents already opened one?
No — only one Cash JISA and one Stocks & Shares JISA can be active per child per tax year. If grandparents already opened a Cash JISA, you can still open a Stocks & Shares JISA but contributions across both must stay under the £9,000 annual limit.
Does the £9,000 JISA allowance count against my own £20,000 ISA limit?
No — JISA allowance is entirely separate. You can fill your full £20,000 adult ISA and contribute £9,000 to each child's JISA in the same tax year.
What happens to a JISA when my child turns 18?
It automatically converts to an adult ISA in the child's name. The child gains full control and can withdraw all funds tax-free. Until then, only the child can withdraw (from age 16 with a Cash JISA) but they cannot withdraw before 18 in most cases.
Cash JISA or Stocks & Shares JISA — which is better for an 18-year-time-horizon?
Historical data: a Stocks & Shares JISA tracking the FTSE All-World over 18 years has outperformed the best Cash JISA by 4-7%/year. For long horizons (10+ years) the consensus is S&S JISA. Cash JISA only makes sense if the child needs the money in < 5 years (e.g. ages 13+).
See how much your child's JISA could grow to age 18. Year-by-year projections, Cash vs Stocks & Shares comparison, and 2025/26 rules.
Junior ISA Growth Calculator
Value at Key Ages
Year-by-Year Growth Table
| Age | Opening Balance | Contribution | Growth | Closing Balance |
|---|
Junior ISA Provider Comparison 2026
| Provider | Type | Annual Fee | Min Contribution | Notes |
|---|---|---|---|---|
| Vanguard | Stocks & Shares | 0.15% (max £375/yr) | £1/month | Index funds only; very low cost |
| Hargreaves Lansdown | Stocks & Shares | 0.45% (capped £45/yr funds) | £25/month | Wide fund choice; good app |
| OneFamily | Stocks & Shares | 1.5% all-in | £10/month | Ethical fund option |
| AJ Bell | Stocks & Shares | 0.25% (max £100/yr) | £25/month | Good for ETFs and funds |
| Coventry BS | Cash | 0% | £1 | Competitive cash rate; check current AER |
| Nationwide | Cash | 0% | £1 | Easy transfers; competitive rate |
| Bath BS | Cash | 0% | £1 | Historically top cash rates |
Rates and fees correct at time of writing. Always check the current rate directly with the provider before opening. You can transfer a JISA to a different provider at any time.
Cash JISA vs Stocks & Shares JISA
| Feature | Cash JISA | Stocks & Shares JISA |
|---|---|---|
| Typical return (2026) | 4–5% AER | 6–10% per year (historical average) |
| Risk of loss | None (FSCS protected up to £85k) | Yes — value can fall short-term |
| Best for | Short timeframes; risk-averse | Long timeframes (5+ years) |
| Inflation protection | Partial (rate may lag inflation) | Better over long run |
| Tax | Tax-free | Tax-free |
| Fees | Usually zero | 0.15–1.5% per year |
| Investment choice | None | Funds, ETFs, shares (varies by provider) |
| Flexibility | Can switch to S&S JISA anytime | Can switch to Cash JISA anytime |
Junior ISA Guide — Rules, Tips & How Compound Growth Works
A Junior ISA (JISA) is a long-term, tax-free savings or investment account for children in the UK. Parents or legal guardians open the account; the child cannot access the money until they turn 18. No income tax or capital gains tax applies to growth inside a JISA — making it one of the most powerful savings vehicles available for building a financial foundation for your child.
JISA Annual Allowance 2025/26
The Junior ISA annual allowance is £9,000 per tax year (unchanged since 2020/21). This limit applies per child, and can be split between a Cash JISA and a Stocks & Shares JISA as long as the combined total does not exceed £9,000. For example, you could put £4,000 in a Cash JISA and £5,000 in a Stocks & Shares JISA in the same tax year.
Who Can Open a Junior ISA?
A JISA can be opened by a parent or legal guardian for a child who is under 18 and a UK resident. The child cannot open their own JISA (though they can manage it from age 16). Grandparents, other relatives and friends can all contribute once the account is open — subject to the £9,000 annual cap in total from all sources.
The Power of Starting Early — Compound Interest Examples
The single most impactful decision with a JISA is starting as early as possible. At 7% annual return:
- £100/month from birth: £18 years x £1,200 = £21,600 contributed — projected value at 18: approximately £43,000+
- £100/month from age 5: 13 years x £1,200 = £15,600 contributed — projected value at 18: approximately £26,000
- £100/month from age 10: 8 years x £1,200 = £9,600 contributed — projected value at 18: approximately £13,800
Starting at birth versus age 10 with the same monthly amount gives more than three times the final value. The five years at the beginning are the most valuable due to compounding on the earliest contributions.
What Happens When the JISA Matures?
On the child's 18th birthday, the JISA automatically becomes a standard adult Cash ISA or Stocks & Shares ISA. The former child (now an adult) takes full control. They can keep contributing (using their £20,000 adult ISA allowance), leave it invested, withdraw the money, or transfer it. The JISA balance does not affect their £20,000 ISA allowance for that tax year.
Child Trust Funds (CTF) and Transferring to a JISA
Children born between 1 September 2002 and 2 January 2011 may have a Child Trust Fund (CTF) rather than a JISA. CTFs and JISAs cannot both be held at the same time, but parents can transfer a CTF to a JISA at any time. This is usually beneficial if the JISA offers better rates or lower fees than the CTF.
Index Trackers in a Stocks & Shares JISA
The most popular investments in Stocks & Shares JISAs are global index tracker funds. The Vanguard FTSE Global All Cap Index Fund and FTSE All-World ETF are widely recommended by financial experts for their diversification, low cost and long-term track record. Vanguard's own JISA charges just 0.15% per year (platform fee plus fund charge), making it one of the most cost-effective options available.
Junior ISA Frequently Asked Questions
What is the Junior ISA allowance for 2025/26?
When can a child access their Junior ISA?
Should I choose a Cash JISA or Stocks & Shares JISA?
Which providers offer the best Junior ISA in 2026?
Can grandparents pay into a Junior ISA?
What happens to a Junior ISA when the child turns 18?
Is there any tax to pay on Junior ISA growth?
How the Junior ISA Calculator Works
This calculator helps you understand your financial position using current UK rates and regulations for the 2025/26 tax year. Whether you are planning savings, evaluating loan options, or projecting investment growth, accurate calculations are essential for making informed decisions about your money.
UK financial products are regulated by the Financial Conduct Authority (FCA). Interest rates, fees, and terms vary significantly between providers, so comparing actual costs rather than headline rates is important. This tool gives you a clear picture to inform your comparisons.
Key Information for 2025/26
The Bank of England base rate is 4.5% as of early 2026. The Personal Savings Allowance lets basic rate taxpayers earn up to £1,000 in savings interest tax-free (£500 for higher rate taxpayers). The annual ISA allowance remains at £20,000, and the Lifetime ISA allowance is £4,000 with a 25% government bonus for first-time buyers or retirement savings.
Example Calculation
Saving £200 per month into an account earning 4.5% AER would grow to approximately £2,454 after one year, including £54 in interest. Over 5 years at the same rate, your £12,000 in contributions would grow to roughly £13,362, earning £1,362 in compound interest.
Source: Based on current UK financial rates. Last updated March 2026.
Official Sources
Data verified against official UK government sources. Last checked April 2026.