JISA Calculator

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Use our JISA calculator to show your children how much their money could be worth when they turn 18 if they invest it in a stocks and shares ISA rather than spend it.

7 % a year
Child invested for 18 years
This is how much the child will be able to withdraw at 18.
This is how much has been paid into a child's JISA.
This is the profits generated from the JISA over the years.

It’s important to remember that investments can go up as well as down so past performance is no indication of future performance.

What is this JISA Calculator for?

The JISA calculator helps you estimate how much a child’s Junior Stocks & Shares ISA could be worth by the time they turn 18. It takes into account how much you put in, how long you invest for, and the growth rate you expect.

It shows:

  • The final JISA value (the projected pot size at 18)
  • The total contributions you made
  • The total returns (how much growth came from investing rather than just saving)

How To Use The Junior Stocks & Shares ISA Calculator

Field What it means Notes
Initial JISA Contribution A one-off lump sum at the start E.g. birthday gift, savings kick-start
Expected Annual Returns The assumed average yearly growth Default is often 5 %. You can try 3 % (cautious) or 7 % (optimistic)
Monthly Contribution Regular savings you add each month E.g. £25, £50, £100
Years Invested How long the account runs until age 18 If child is 2, enter 16 (to reach 18)

JISA Calc Step-by-Step Use

Enter an initial contribution (or £0 if none).

  1. Set your expected annual return.
  2. Enter how much you’ll add each month.
  3. Input the years invested (up to 18 total).
  4. Click calculate to see: Final Value, Total Contributions & Total Returns

You can adjust the numbers to compare scenarios (e.g. £25/month vs £100/month, or 4 % vs 7 % growth).

Key Things to Know About Our Junior Stocks & Shares ISA Calculator

Unlike Junior SIPPs, JISA money becomes accessible at 18, not locked away until retirement.

The annual JISA allowance (2025/26) is £9,000 per child — you can’t contribute more than this each tax year.

Growth and withdrawals are tax-free.

The calculator does not include fees (fund charges, platform costs).

A Real World Example Of How Much A Junior Stocks & Shares ISA Can Generate

Say you open a JISA for your child at birth with:

  • £1,000 initial contribution
  • £100 per month
  • 7 % annual returns
  • 18 years invested

By the time they turn 18, the calculator shows:

  • Total Contributions: £22,600
  • Final JISA Value: ~£38,700
  • Total Returns (growth): ~£16,100

So your £22,600 of savings could potentially turn into nearly £39,000, completely tax-free, giving them a strong financial head start at adulthood.

Ready to open a Junior Stocks & Shares ISA?

You can compare the best JISA accounts using our Junior stocks and shares comparison table below:

Good Money Guide has tested and ranked the best junior stocks and shares ISA providers and accounts in the UK that are regulated by the FCA.
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