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ISA vs JISA

Compare a Junior ISA (JISA) vs an adult ISA projection to age 18 using simple, adjustable assumptions.

EducationalTax wrappersContributionsCompounding
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Educational tool (not financial advice)

This calculator is for learning and scenario planning. It does not consider your full circumstances and does not recommend specific products or providers.

Assumptions matter

Small changes in growth, inflation, fees and time horizons can change outcomes materially. Use the inputs to explore a range of scenarios.

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Inputs

Years to 18: 15

Capped at ~£750 / month (annual cap £9,000).

Capped at ~£1666 / month (annual cap £20,000).

Starting balances (optional)

Results (projection to age 18)

JISA
£26,729
Monthly used: £100
Adult ISA
£53,458
Monthly used: £200

Period: 15 year(s) to age 18.

Growth: 5% nominal, monthly compounding.

JISA funds are typically locked until 18; an adult ISA is generally accessible, but requires discipline.

What this shows (simple)

  • Both wrappers can grow tax-free inside the ISA/JISA.
  • JISA has a smaller allowance, but can ring-fence money until 18.
  • Adult ISA has a larger allowance and access, but needs self-control.
▼ Assumptions & methodology
  • Growth is an assumed nominal annual rate, compounded monthly.
  • Contributions are capped to the annual allowance ÷ 12 for each wrapper.
  • This does not model inflation, fees, tax changes, provider charges, or market volatility.
  • Results are for learning and comparison only.

Fees - Coming soon!.

Privacy

This tool runs in the browser. It does not need personal data inputs to be useful.

Last reviewed: (add date)• Tags: Educational, Tax wrappers, Contributions, Compounding
Related: Programmes • Insights