Junior ISA Growth Calculator
Project a Junior ISA value at age 18 from current balance, monthly contributions, annual allowance, growth, fees and inflation.
Enter Junior ISA Assumptions
Projected Value At 18
Estimated Junior ISA value at age 18.
What A Junior ISA Projection Shows
A Junior ISA can hold cash, stocks and shares, or both, depending on the provider and eligibility. The calculator projects a balance at age 18 from regular and annual contributions, assumed growth and fees. It also checks the entered annual contribution against the Junior ISA allowance. The 2026/27 Junior ISA allowance is GBP 9,000, according to GOV.UK guidance. The projection is useful for planning gifts from parents, grandparents and relatives, but it cannot promise a future value.
Formula Method
Years to age 18 = 18 - current ageAnnual contribution = monthly contribution x 12 + extra annual contributionNet annual growth rate = expected growth rate - annual feeProjected value = balance grown monthly plus contributions grown over timeEstimated gain = projected value - current balance - future contributionsInflation-adjusted value = projected value / (1 + inflation rate) ^ yearsThe calculator compounds monthly using a simplified net growth rate. That is a planning approximation, not the exact method used by every provider. Real investment returns are uneven, and charges can be taken monthly, yearly or inside funds. Cash Junior ISA interest rates can change. Stocks and shares Junior ISAs can lose value, particularly over short periods. If contributions exceed the entered allowance, the warning line shows that the plan needs adjustment or confirmation against current rules.
Contribution Scenarios
| Monthly Contribution | Annual Total | Allowance Position | Planning Note |
|---|---|---|---|
| GBP 25 | GBP 300 | Within GBP 9,000 | Small regular habit. |
| GBP 50 | GBP 600 | Within GBP 9,000 | Common family gift plan. |
| GBP 100 | GBP 1,200 | Within GBP 9,000 | Meaningful long-term saving. |
| GBP 250 | GBP 3,000 | Within GBP 9,000 | Higher regular family saving. |
| GBP 500 | GBP 6,000 | Within GBP 9,000 | Leaves room for gifts. |
| GBP 750 | GBP 9,000 | At GBP 9,000 | No extra annual contribution room. |
Worked Junior ISA Example
A child aged 5 has a Junior ISA balance of GBP 2,500. The family contributes GBP 150 per month and adds GBP 500 once a year. That is GBP 2,300 per year, within the GBP 9,000 allowance. With a 5% growth assumption and 0.5% fee, the simplified net rate is 4.5% per year. By age 18, the projected value is around GBP 44,000. Future contributions are about GBP 29,900, so the estimated growth after fees makes up the rest. With 2.5% inflation, the spending power in today’s money is lower than the headline projection.
Cash Or Stocks And Shares
A cash Junior ISA may suit families who want lower volatility, but interest rates can fall and inflation can erode value. A stocks and shares Junior ISA may offer higher long-term potential, but the value can drop and the child may reach 18 during a market downturn. The right choice depends on time horizon, risk tolerance, other savings, fees and whether the family can accept short-term falls. This calculator lets users test growth and fee assumptions, but it does not choose a product.
Ownership And Access At 18
Money in a Junior ISA belongs to the child. A registered contact manages the account while the child is young, but the child can usually take control at 16 and access the money at 18. Parents cannot reclaim the money because plans change. That is a benefit for long-term saving, but it is also a responsibility. Before paying in large sums, consider emergency savings, sibling fairness, university plans, disability needs, housing goals and whether a bare trust or other arrangement needs advice.
Allowance Coordination
The allowance applies to the child, not to each adult who contributes. If parents, grandparents and relatives all pay in, someone needs to track the total across cash and stocks and shares Junior ISA accounts. A birthday gift, regular standing order and one-off family transfer can easily overlap. Keep a simple annual contribution log with date, payer, amount, provider and remaining allowance. If the family is near the limit, check the provider record before sending more money.
For regular saving, review the standing order each April when the tax year changes. A monthly amount that was fine last year may leave less room for one-off gifts this year. Keep sibling contributions separate so fairness is visible. Record transfers between providers as well.
FAQs
What is the Junior ISA allowance for 2026/27?
GOV.UK guidance shows the Junior ISA allowance as GBP 9,000 for the 2026/27 tax year. Always check current guidance before paying in large amounts.
Who owns the money in a Junior ISA?
The money belongs to the child. A registered contact manages the account until the child can take control under the scheme rules.
Can parents withdraw Junior ISA money?
Normally no. The money is locked until the child reaches 18, except in specific circumstances such as terminal illness or death.
Is a stocks and shares Junior ISA safe?
It has investment risk. The value can fall as well as rise, and fees affect returns. Cash has lower investment risk but may lag inflation.
What happens if contributions exceed the allowance?
The provider or HMRC rules may require correction. The calculator shows a warning, but it does not manage subscriptions across providers.
Can grandparents pay into a Junior ISA?
Yes, family and friends can usually contribute, but all payments count toward the child’s annual Junior ISA allowance.
Sources
- HM Revenue & Customs. (2026). Individual Savings Account (ISA) statistics and guidance: 2026 to 2027 allowances. GOV.UK. https://www.gov.uk/individual-savings-accounts/junior-isas
- MoneyHelper. (n.d.). Junior ISAs. MoneyHelper. https://www.moneyhelper.org.uk/en/savings/types-of-savings/junior-isas
- Financial Conduct Authority. (n.d.). Investing and risk. FCA. https://www.fca.org.uk/consumers/investing