Junior ISA Calculator 2026/27

A Junior ISA is a tax-free savings or investment account for under-18s. Anyone can pay in (parents, grandparents, friends) up to the annual limit of £9,000.

• The child can't access the money until age 18 (then it becomes theirs unconditionally).
• Two types: Cash JISA (fixed-rate savings) and Stocks & Shares JISA (investments).
• You can split contributions across both types in the same tax year, up to the £9,000 total.
• Only one Cash JISA and one S&S JISA per child at a time.
• The adult ISA minimum age has been 18 for every ISA type since 6 April 2024, so a 16 or 17-year-old cannot open one alongside a JISA.

For a JISA opened at age 0, the money is locked away for 18 years. That's long enough that historical equity returns (~6-7% nominal, after CPI ~3-4% real) overwhelm any short-term volatility.

At 4% cash vs 7% equity over 18 years, £100/month grows to roughly £31k vs £43k respectively, a £12k difference, all of it tax-free. The shorter the time horizon, the smaller the case for equities.