How Cash ISAs Work
An Individual Savings Account (ISA) is a tax-free savings wrapper available to all UK residents aged 16 or over (18 for Lifetime ISAs and stocks and shares ISAs). The key advantage is simple: any interest you earn inside a cash ISA is completely free from income tax. For the 2025/26 tax year, the total ISA allowance is £20,000. You can split this between different types of ISA — cash, stocks and shares, innovative finance, and Lifetime — but the total across all types cannot exceed £20,000 in a single tax year.
Easy Access vs Fixed Rate
Easy access ISAs let you withdraw money at any time without penalty, but rates can change. Fixed rate ISAs lock your money away for a set period (typically one to five years) in exchange for a guaranteed rate. If you are unlikely to need the money, fixed rate ISAs typically offer higher returns. Some providers charge penalties for early withdrawal from fixed rate accounts — always check the terms before committing.
Lifetime ISAs (LISAs)
Lifetime ISAs are available to those aged 18 to 39. You can save up to £4,000 per year (which counts towards your £20,000 total ISA allowance) and the government adds a 25% bonus — up to £1,000 per year. The money can be used for your first home purchase (up to £450,000) or withdrawn after age 60. Withdrawing for any other reason incurs a 25% penalty, which means you actually lose money compared to what you put in. LISAs are excellent for first-time buyers but require commitment.
Tax-Free Status
Since April 2016, most savers also benefit from the Personal Savings Allowance (PSA), which lets basic rate taxpayers earn £1,000 in interest tax-free outside an ISA, or £500 for higher rate taxpayers. Additional rate taxpayers get no PSA. If your savings are large enough that you would exceed the PSA, a cash ISA becomes particularly valuable. Even if you are within the PSA now, an ISA protects you against future rate rises or changes to the allowance.
Tips for Choosing the Right ISA
- Compare AER (Annual Equivalent Rate), not headline rates — AER accounts for compounding and lets you compare fairly
- Check whether bonus rates are included. Some providers offer a high initial rate that drops after 12 months
- Consider whether you need access to your money. If not, a fixed rate ISA will almost always pay more
- Use your full £20,000 allowance if you can — unused allowance cannot be carried forward to the next tax year
- From 2024/25, you can pay into multiple ISAs of the same type in a single tax year (previously limited to one per type)
- All ISA deposits are protected up to £85,000 per provider by the Financial Services Compensation Scheme (FSCS)