Junior ISA calculator
What a few pounds a month becomes by 18.
Every calculator promises a number at the end. This one shows what starting from day one is worth by their eighteenth birthday, and how much waiting even a few years quietly costs.
Your plan
Capped at £750 a month - the Junior ISA limit split evenly across the year.
Optional - anything already saved in the Junior ISA.
On their 18th birthday
On their 18th birthday the Junior ISA would be worth £21,536. You would have paid in £10,800; growth would add £10,736.
£10,800
£10,736
That money is the child’s from the day they turn 18, to spend, save or invest however they choose.
Starting now vs starting later
Wait 5 years before opening the account and this is what it costs by their 18th birthday.
That’s what waiting 5 years costs them, same monthly amount, same rate, just started later.
| Year | Start now | Wait 5 years |
|---|---|---|
| 0 | £0 | £0 |
| 1 | £620 | £0 |
| 2 | £1,284 | £0 |
| 3 | £1,997 | £0 |
| 4 | £2,760 | £0 |
| 5 | £3,580 | £0 |
| 6 | £4,458 | £620 |
| 7 | £5,400 | £1,284 |
| 8 | £6,410 | £1,997 |
| 9 | £7,493 | £2,760 |
| 10 | £8,654 | £3,580 |
| 11 | £9,899 | £4,458 |
| 12 | £11,235 | £5,400 |
| 13 | £12,667 | £6,410 |
| 14 | £14,202 | £7,493 |
| 15 | £15,848 | £8,654 |
| 16 | £17,613 | £9,899 |
| 17 | £19,506 | £11,235 |
| 18 | £21,536 | £12,667 |
How this works
Assumes the Junior ISA grows at 7% a year, compounded monthly, with contributions added at the end of each month, up to the Junior ISA limit of £9,000 (2026 to 2027 tax year). Real returns vary and aren’t guaranteed. This is an illustration, not a prediction. This is not financial advice. These are ideas to make you a little bit richer.
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