Junior ISAs are tax-free savings accounts for children under age 18. You can save £4,128, tax-free, into a junior ISA. The amount you can save changes every tax year, which runs from 6 April to 5 April. The junior ISA limit for tax year 2017/18 is £4,128. Junior ISAs replace child trust funds (CTFs), which the government no longer provides – although if you have a CTF, you can continue with it.