Cash ISA or Stocks and Shares ISA? Choosing What to Do With £20,000

The annual ISA allowance can still be used entirely for cash. After the planned reduction was reversed, savers can continue to put up to £20,000 a year into cash ISAs, or divide that allowance between cash and other ISA types. For anyone who already deposited the full amount in cash, the choice now is whether that money suits their needs and time horizon.

The change matters because some savers had treated the 2026/27 tax year as their last chance to put the full £20,000 allowance into cash. The planned rule would have limited cash ISA contributions to £12,000 per tax year for people under 65 from April 2027. That plan has been dropped. Cash ISA deposits reached a record £57 billion in 2025, according to the Bank of England.

Keep cash for emergencies and near-term plans

Cash has a clear role in a household’s finances. An accessible emergency fund can help cover unexpected bills without needing to sell investments or borrow. The source recommends keeping three to six months of essential spending in an easy-access savings account.

Cash can also suit money earmarked for a known expense in the near future, such as a car or wedding. Its value won’t fall with market movements, which can matter when there isn’t time to wait for an investment to recover. The trade-off is that money left in cash may have less opportunity to grow over longer periods.

Andy Reed, head of behavioural economics research at Vanguard, described cash beyond short-term needs as an opportunity cost: savers may miss out on gains they could have earned by investing. That trade-off is relevant in the UK, where cash ISAs are more common than stocks and shares ISAs. In the 2024/25 tax year, almost 17 million adult ISA accounts were subscribed to: 10.7 million were cash ISAs and 4.9 million were stocks and shares ISAs.

Compare the time horizon, not just the headline figures

A five-year fixed-rate cash ISA paid 5.25% at the end of October 2026. At that rate, £20,000 would earn £5,989 in tax-free interest over five years. That gives a useful example of the return a saver might receive from a fixed rate, though access to the money is restricted during the term.

By comparison, the S&P 500, an index tracking 500 of the largest US companies, delivered average annualised returns of around 13% over the preceding five years. If £20,000 had earned that rate for five years, it would have grown to £38,177, or £18,177 more than the original amount, before fees. In a stocks and shares ISA, gains and dividends are sheltered from capital gains tax and dividend tax.

Those figures describe different kinds of outcomes. The cash example uses a fixed rate for a defined term; the investment example uses past market performance, which can’t predict future results. Investment values can fall as well as rise, and fees reduce returns. A five-year period with strong average returns doesn’t mean an investor will earn 13% each year, or receive their original £20,000 back if they need to sell after a market drop.

Time matters. Helen Morrissey, head of retirement analysis at Hargreaves Lansdown, said cash may be more suitable if someone expects to need the money within three years. If the money can remain invested for at least three years, she said, investing could be considered, provided the saver understands the risks and is comfortable with their investments. The source also says investors are generally advised to stay invested for at least five to ten years.

So a large gap between the example cash interest and investment growth isn’t enough on its own to decide. Money needed soon may be better kept accessible and stable. Money intended for a longer-term goal may have more time to ride out market falls, but its value can still decline and there’s no guaranteed return.

Transfer ISA money without withdrawing it

If you decide that some cash ISA savings belong in a stocks and shares ISA, you can request a transfer without using more of your annual allowance. Contact the provider you want to move to and ask it to arrange the transfer. It will provide a transfer form, and the process generally takes longer than moving money between ordinary bank accounts.

Don’t withdraw the money yourself and then pay it into another ISA. A withdrawal removes money from the ISA’s tax-free status and, unless the account is flexible, doesn’t restore the allowance you already used. For example, someone who paid £20,000 into a cash ISA during 2026/27 and then withdrew it would have no allowance left that year to pay that sum into a stocks and shares ISA.

Before starting, check with both the existing provider and the new one for any transfer restrictions. Following their ISA transfer process keeps the money within the ISA system while it moves. Your practical decision is then about the purpose of the savings: keep cash for stability and nearer-term spending, or consider investments for money you can leave untouched through market ups and downs.