The short version
- A Junior ISA lets you invest up to £9,000 a year for a child, free of tax. The money is theirs, and they can't take it out until they turn 18.
- £20 a month into an S&P 500 ETF from January 2011 would have been worth £14,454 at the end of September 2026, from £3,780 paid in. In a FTSE 100 ETF it would have been £7,825, and in a world ETF £11,583.
- £1,000 put in at birth in January 2011 would have become £9,154, £3,166 or £6,061 in the same three funds.
- The S&P 500's lead came from an unusually strong run for big US companies and a weaker pound. Neither is guaranteed to repeat.
- At 18 the account becomes an adult ISA in the child's name. Left invested, the money can keep growing for decades.
- £9,000the most that can go into a child's Junior ISAs each tax year (2026/27)
- £14,454£20 a month into an S&P 500 ETF since January 2011, from £3,780 paid in
- 18the age the money becomes the child's, as an adult ISA
The calculator
Choose when your child was born, what went in at birth and what goes in each month. The first chart uses real prices of three accumulating ETFs up to the end of September 2026, so it shows what actually happened. The second carries today’s value forward to 18, 30 and 65 at a growth rate you choose.
Junior ISA calculator
So far: what it would be worth now
Real month-end prices of three ETFs, from the birth month to the end of September 2026, after the funds' own charges.
Where it could get to
A projection, not a promise: today's value carried forward at a steady growth rate after inflation, with the monthly payments continuing (rising with prices) until 18 and then stopping. Figures are in today's money.
Every year group since 2011
The younger the child, the less time the money has had, so the gap between what went in and what it’s worth is smaller. For children born in the last two or three years, a fall in prices could still leave the pot below what was paid in. That is normal for money invested in shares, and it is why time matters more than the fund.
£20 a month from birth: every year group since 2011
What £20 a month, paid in from each January since 2011, was worth at the end of September 2026. Hover over, tap or tab to a year for the figures.
Show the data, including £1,000 at birth
| Born | Paid in (£20 a month) | £20 a month: S&P 500 ETF | £20 a month: FTSE 100 ETF | £20 a month: World ETF | £1,000 at birth: S&P 500 ETF | £1,000 at birth: FTSE 100 ETF | £1,000 at birth: World ETF |
|---|---|---|---|---|---|---|---|
| January 2011 | £3,780 | £14,454 | £7,825 | £11,583 | £9,154 | £3,166 | £6,061 |
| January 2012 | £3,540 | £12,250 | £7,058 | £10,094 | £8,683 | £3,169 | £6,175 |
| January 2013 | £3,300 | £10,272 | £6,315 | £8,657 | £7,490 | £2,775 | £5,356 |
| January 2014 | £3,060 | £8,672 | £5,681 | £7,480 | £6,416 | £2,595 | £4,793 |
| January 2015 | £2,820 | £7,266 | £5,087 | £6,411 | £5,136 | £2,410 | £4,079 |
| January 2016 | £2,580 | £6,056 | £4,502 | £5,446 | £4,980 | £2,595 | £4,090 |
| January 2017 | £2,340 | £5,027 | £3,935 | £4,590 | £3,665 | £2,124 | £3,077 |
| January 2018 | £2,100 | £4,195 | £3,452 | £3,894 | £3,257 | £1,935 | £2,754 |
| January 2019 | £1,860 | £3,441 | £2,987 | £3,247 | £3,118 | £2,003 | £2,727 |
| January 2020 | £1,620 | £2,775 | £2,540 | £2,657 | £2,567 | £1,836 | £2,317 |
| January 2021 | £1,380 | £2,166 | £2,025 | £2,098 | £2,280 | £2,021 | £2,080 |
| January 2022 | £1,140 | £1,689 | £1,586 | £1,653 | £1,845 | £1,679 | £1,766 |
| January 2023 | £900 | £1,247 | £1,186 | £1,226 | £1,844 | £1,558 | £1,744 |
| January 2024 | £660 | £829 | £813 | £823 | £1,556 | £1,523 | £1,523 |
| January 2025 | £420 | £494 | £475 | £490 | £1,202 | £1,294 | £1,222 |
| January 2026 | £180 | £195 | £183 | £192 | £1,157 | £1,060 | £1,138 |
Why the S&P 500 did so much better
From October 2010 to September 2026, the S&P 500 ETF grew by 15.4% a year in pounds, the world ETF by 12.4% and the FTSE 100 ETF by 7.7%. Two things explain most of the gap. The biggest US companies, mostly technology firms, grew their profits and share prices far faster than the banks, oil companies and miners that dominate the FTSE 100. And the pound fell from 1.58 dollars to 1.33, which on its own added about 1.1% a year to anything held in dollars.
Neither is a law of nature. In the ten years to the end of 2009, the S&P 500 lost 9% in dollars, even with dividends reinvested. A child’s pot will be invested for 18 years or more, and nobody knows which market will lead over that stretch. That is the case for a world ETF, which holds both and everything in between. Global, FTSE 100 or S&P 500? and Home bias go through the evidence.
How a Junior ISA works
- Who can have one: any child under 18 living in the UK who doesn’t have a Child Trust Fund (GOV.UK). A parent or guardian opens it for a child under 16; at 16 or 17 the child can open their own.
- How much: up to £9,000 a tax year in total, across both kinds of Junior ISA. Anyone can pay in, so grandparents’ birthday money counts towards the same £9,000 (GOV.UK). The limit is frozen at £9,000 until April 2031 (Budget 2025).
- Cash or investments: a child can have one cash Junior ISA and one stocks and shares Junior ISA, or both (GOV.UK). ETFs go in the stocks and shares kind.
- No tax: no tax on interest, dividends or growth.
- Whose money: the child’s. Payments are gifts, and they can’t be taken back. The child can take control at 16 but can’t withdraw anything until 18 (GOV.UK). The only early exits are if the child is terminally ill or dies (GOV.UK).
- Parents’ tax: normally, if money a parent gives a child earns more than £100 a year, the parent pays tax on it. That rule doesn’t apply to a Junior ISA (GOV.UK).
Grandparents who pay in can use their inheritance tax allowances: up to £3,000 of gifts a year, regular gifts out of income that don’t affect their standard of living, and small gifts of up to £250 a person (GOV.UK).
18, 30, 65: what happens to the money
At 16 the child can run the account themselves. Since April 2024 they can no longer open an adult cash ISA at 16 or 17: you must be 18 for any adult ISA (HMRC).
At 18 the Junior ISA turns into an adult ISA in their name, automatically (GOV.UK). The money stays tax-free for as long as it stays in an ISA, and it’s theirs to spend, keep or move. Nobody else can stop them taking it out. That’s worth talking about before their 18th birthday.
After 18 they can add up to £20,000 a year of their own. Between 18 and 39 they can also open a Lifetime ISA, where the government adds 25% to up to £4,000 a year for a first home or later life (GOV.UK); Budget 2025 said a simpler first-time buyers’ ISA will replace it (Budget 2025).
At 30 or 65 nothing happens automatically. Those ages are in the calculator to show what time does: money left invested from 18 to 65 has 47 more years to grow, and in the projection that matters far more than anything paid in.
If you want money that can’t be touched until later life, a pension is the other option. You can pay up to £2,880 a year into a pension for a child, and tax relief tops it up to £3,600 (GOV.UK). It can’t be taken out until 57 at the earliest under current rules (GOV.UK).
Born between 2002 and 2011? Check for a Child Trust Fund
Children born between 1 September 2002 and 2 January 2011 were given a Child Trust Fund, usually with a £250 government payment at birth, or £500 for lower-income families and children in care (GOV.UK, the 2004 regulations). If parents didn’t open one, HMRC did. About 6.3 million were opened (HMRC).
A child can’t have a Junior ISA and a Child Trust Fund at the same time, but you can transfer a Child Trust Fund into a Junior ISA (GOV.UK). At 18 it matures and can be taken out or moved to an adult ISA (GOV.UK).
Many never are. In April 2026 about 827,000 matured Child Trust Funds were still sitting unclaimed, worth £2,310 on average (HMRC Annual Savings Statistics 2026), about £1.9 billion in total (HMRC CTF Table 1a). HMRC’s free Child Trust Fund finder tells you where an account is. You don’t need to pay a company to find it.
How many families use them
About 1.6 million Junior ISA accounts were paid into in 2024/25, and £2.5 billion went in, according to HMRC (Annual Savings Statistics 2026). Around 38% of the money went into cash. The average account received £1,570 in the year, or £2,075 in stocks and shares Junior ISAs. By April 2025, Junior ISAs held £14.1 billion, £8.4 billion of it in stocks and shares (HMRC ISA Tables 9.4 and 9.6).
| Tax year | Accounts paid into | Of which stocks and shares | Paid in | Average per account |
|---|---|---|---|---|
| 2019/20 | 1.02 million | 317k | £971m | £949 |
| 2020/21 | 0.95 million | 287k | £1.24 billion | £1,297 |
| 2021/22 | 1.21 million | 475k | £1.49 billion | £1,229 |
| 2022/23 | 1.25 million | 489k | £1.52 billion | £1,220 |
| 2023/24 | 1.37 million | 598k | £1.84 billion | £1,347 |
| 2024/25 (provisional) | 1.60 million | 749k | £2.52 billion | £1,570 |
HMRC counts accounts, not children: a child with both kinds counts twice. 2024/25 figures are provisional. Source: HMRC Annual Savings Statistics 2026, ISA Table 9.4.
Where to open one
Most investment platforms offer a stocks and shares Junior ISA, but not all: Trading 212 and InvestEngine don’t. Some charge less on a Junior ISA than on an adult one; Hargreaves Lansdown, for example, has no account charge or online dealing charge on it. UK investment platforms compared shows which offer one and what they charge.
How the calculator works
The look-back uses the month-end prices of three accumulating ETFs listed in London: iShares Core S&P 500 (CSP1), iShares Core FTSE 100 (CUKX) and iShares Core MSCI World (SWDA). Because they’re accumulating, dividends are reinvested inside the fund and its charges are already taken off. The sum at birth and the first monthly payment go in at the end of the birth month; later payments at the end of each month. Platform fees and the small cost of buying aren’t included. Prices come from Yahoo Finance; only the results are published.
The projection starts from today’s value and grows it at a steady rate after inflation, so the figures are in today’s money. Monthly payments are assumed to rise with prices until 18 and then stop. Real returns come in an uneven sequence, with falls along the way, and the 3% to 7% range is an illustration, not a forecast. Over the long run, UK shares have returned about 5% a year after inflation: the returns explorer lets you check any period since 1871.
Common questions
- How much should I put in a Junior ISA?
- Whatever you can keep up. The calculator shows that small amounts started early add up, and that the sum at birth often matters as much as the monthly payments. The limit is £9,000 a year from everyone combined.
- Is an S&P 500 ETF the best choice for a child?
- It did best over these 15 years, but that isn’t a reason to expect it to keep doing so. A world ETF spreads the money across more than 1,000 companies in many countries, including the US. This site doesn’t recommend funds.
- Can I take money out of my child’s Junior ISA?
- No. It belongs to the child and stays locked until they’re 18, unless they are terminally ill or die.
- What happens to a Junior ISA at 18?
- It becomes an adult ISA in their name automatically. They can leave it invested, add to it, or take it out.
- Can grandparents pay into a Junior ISA?
- Yes. Anyone can, as long as the total from everyone stays within £9,000 a tax year. Only a parent or guardian can open it for a child under 16.
- My child was born before 2011. Can they have one?
- Only by moving their Child Trust Fund into a Junior ISA, because a child can’t hold both. The calculator starts in January 2011 for that reason.
This calculator shows what happened in the past and a simple projection. It isn't a forecast or a recommendation to use any fund or account. Investments can fall as well as rise, and you may get back less than you put in. Read the full disclaimer.
Sources
- Junior Individual Savings Accounts (ISA), GOV.UK, including the pages on opening, adding money, managing and terminal illness
- Budget 2025, HM Treasury, 26 November 2025; Tax-free savings newsletter 19, HMRC, November 2025
- Who can invest in an ISA if you are an ISA manager, HMRC
- Savings for children, GOV.UK
- Inheritance Tax: gifts, GOV.UK
- Lifetime ISA, GOV.UK
- Tax on your private pension: pension tax relief, GOV.UK; Increasing normal minimum pension age, HM Treasury
- Child Trust Funds, GOV.UK, including Find a Child Trust Fund
- The Child Trust Funds Regulations 2004, regulation 7, legislation.gov.uk
- Government steps up drive to reconnect young people with unclaimed savings, HMRC, 29 June 2026
- Annual Savings Statistics 2026, HMRC, 16 September 2026: commentary, ISA tables (Tables 9.4 and 9.6) and Child Trust Fund tables (Table 1a)
- Month-end closing prices of CSP1, CUKX and SWDA (London listings), October 2010 to September 2026, from Yahoo Finance. GBP/USD exchange rate from Yahoo Finance.
- S&P 500 Total Return index, end of 1999 to end of 2009, from Yahoo Finance.
Calculator data to the end of September 2026. Rules checked on 20 October 2026.