An ISA is one of those things that sounds more complicated than it actually is. The acronym stands for Individual Savings Account, but the important bit is not the account itself. It is the tax wrapper.
Everything inside an ISA grows free of income tax and capital gains tax. Any interest you earn, any investment growth, any dividends — the taxman does not touch them. Outside an ISA, you would pay tax on those gains once they exceed your Personal Savings Allowance (£1,000 for basic-rate taxpayers, £500 for higher-rate). Inside an ISA, there is no limit. You could have £500,000 in an ISA generating £30,000 a year in returns and you would owe nothing in tax on it.
The current annual ISA allowance is £20,000. That is the maximum you can put into ISAs in a single tax year (6 April to 5 April). You can split it across different types of ISA, but the total across all of them cannot exceed £20,000. Any allowance you do not use is lost — it does not roll over to the next year.
If £20,000 sounds like a figure that is irrelevant to someone on a starter salary, you are right that it probably is for now. But the allowance is there for the future, and even small amounts benefit from being inside the tax-free wrapper. There is no minimum to open most ISAs. Some platforms let you start with £1.
The Four Types of ISA
Cash ISA
What it is: A savings account where the interest is tax-free.
Who it suits: Anyone building a rainy-day fund, saving for something specific within the next one to three years, or who wants zero risk on their money.
How it works: Exactly like a normal savings account, except the interest is not taxable. You can get easy-access Cash ISAs (withdraw any time) or fixed-rate Cash ISAs (lock your money away for a set period, usually one to five years, in exchange for a higher rate).
The catch: Interest rates on Cash ISAs often lag behind the best non-ISA savings accounts. And since the Personal Savings Allowance already shelters £1,000 of interest from tax for basic-rate taxpayers, a Cash ISA only offers a genuine tax advantage once your total savings interest (across all accounts) exceeds that £1,000 threshold. For most young people starting out, the Personal Savings Allowance covers them, and the best move is simply to find the highest interest rate available, ISA or not.
When it matters: Cash ISAs become more valuable as your savings grow, as interest rates rise, or if you move into the higher-rate tax band (where the Personal Savings Allowance drops to £500). They also protect against future changes to the Personal Savings Allowance, which the government could reduce or abolish.
Stocks and Shares ISA
What it is: An investment account where all growth, dividends, and gains are tax-free.
Who it suits: Anyone investing for five years or more. This is the ISA that builds serious long-term wealth.
How it works: You open the ISA with an investment platform (Vanguard, InvestEngine, AJ Bell, Hargreaves Lansdown, Trading 212, and others all offer them). You deposit money, then choose what to invest in. The simplest and most widely recommended starting point is a global index fund, a US index fund, or a UK index fund. These track a broad market index, giving you automatic diversification across hundreds or thousands of companies in a single purchase. A global fund gives you the broadest spread. A US fund gives you exposure to the market that has consistently outperformed the UK over the long term, though it comes with currency risk: if the pound strengthens against the dollar, your returns are worth less when converted back to sterling, and vice versa. A UK fund avoids that currency risk but limits you to a market that represents only about 4% of global stock market value. For most beginners, a global index fund is the best starting point because it includes a significant US weighting alongside everything else.
Why it matters for young people: Over the long term, the stock market has historically returned around 7 to 8% per year on average before inflation (roughly 4 to 5% after). Cash savings accounts have frequently failed to beat inflation over sustained periods. If you are putting money away for 10, 20, or 40 years, the difference between cash returns and equity (stocks and shares) returns is enormous. I cover the maths in detail in the Time — The Money Superpower eBook.
Fees to watch: Platform fees (what the provider charges for holding your ISA) and fund fees (what the investment fund charges for managing it). For index funds, total costs can be as low as 0.15 to 0.30% per year. That sounds tiny, but over decades, the difference between paying 0.2% and 1.5% in annual fees can cost you tens of thousands of pounds. Always check the total cost before investing.
The risk: Your investments can go down as well as up. In a bad year, your ISA might lose 20% or more. If you need the money within one to three years, a stocks and shares ISA is not appropriate. If you have five years or more, history strongly favours equities over cash, but there are no guarantees, and past performance is not a reliable indicator of future results.
Lifetime ISA (LISA)
What it is: A savings or investment ISA with a 25% government bonus, designed for buying a first home or retirement.
Who it suits: Anyone aged 18 to 39 who is saving for a first property or wants an additional retirement savings vehicle.
How it works: You can save up to £4,000 per year into a LISA (this counts within your overall £20,000 ISA allowance). The government adds 25% on top. Put in £4,000, get a £1,000 bonus. That is a guaranteed 25% return before any interest or investment growth — something no other savings product offers.
The LISA can be a cash LISA (works like a savings account with the bonus on top) or a stocks and shares LISA (works like an investment ISA with the bonus on top).
The restrictions: You can only withdraw penalty-free for two purposes: buying your first home (property value up to £450,000) or after you turn 60. Withdrawing for any other reason incurs a 25% penalty on the withdrawal amount. Crucially, that 25% is taken from the full amount including the bonus, which means you actually lose some of your own contributions too. If you put in £4,000 and received a £1,000 bonus (total £5,000), then withdrew the lot early, the penalty would be £1,250 — leaving you with £3,750, which is £250 less than you put in.
My view: If you are under 40 and think you will buy a first home at some point, the LISA bonus is the best guaranteed return available. Open one, even if you can only put £50 a month in. But understand the withdrawal penalty thoroughly before you commit, and do not put money in that you might need for other purposes before you buy.
Innovative Finance ISA (IFISA)
What it is: An ISA wrapper around peer-to-peer lending or similar alternative finance investments.
Who it suits: Experienced investors who understand the risks of peer-to-peer lending and want the interest to be tax-free.
My view: This is not one for beginners. The returns can be higher than cash, but so is the risk. Peer-to-peer platforms can and do fail. Your capital is not protected by the FSCS in the way that cash deposits are. Unless you have already maximised your other ISA options and understand exactly what you are investing in, I would leave this one alone.
How to Split Your Allowance
The £20,000 annual allowance can be divided across ISA types however you choose, with one rule: you can only pay into one of each type per tax year (one Cash ISA, one stocks and shares ISA, one LISA, one IFISA).
For most young people starting out, a sensible split might be:
If you have no rainy-day fund yet: Put everything into a Cash ISA (or a standard savings account if the rate is better) until you have three to six months of living costs saved. Then redirect future savings into a stocks and shares ISA for long-term growth.
If you have a rainy-day fund and are saving for a first home: Open a LISA and put up to £4,000 a year into it for the 25% bonus. Anything beyond that goes into a stocks and shares ISA.
If you have a rainy-day fund and no plans to buy soon: Put as much as you can into a stocks and shares ISA in a low-cost global index fund. Time in the market matters more than timing the market, and starting early, even with small amounts, is what makes the compounding work.
Common Questions
Can I withdraw from a stocks and shares ISA? Yes. Unlike a pension, your money is not locked away. You can sell investments and withdraw cash at any time. However, be aware that once you withdraw, you may lose that portion of your annual allowance (depending on whether your ISA is “flexible” — check with your provider).
What happens if I do not use my full £20,000 allowance? It is gone. The allowance does not carry over. If you only invest £2,000 this year, you cannot invest £38,000 next year. Each year starts fresh at £20,000.
Can I transfer between ISA types? Yes. You can transfer from a Cash ISA to a stocks and shares ISA (or vice versa) without it counting against your current year’s allowance. Contact the receiving provider to arrange the transfer — do not withdraw and redeposit, as that would use up your annual allowance.
Do ISAs affect my benefits or student loan? ISA savings and growth do not count as income for student loan repayment purposes. For means-tested benefits, savings above £6,000 (including ISAs) may affect your entitlement, and savings above £16,000 will usually disqualify you from most means-tested benefits. This is worth checking if you are currently claiming.
The One Thing to Remember
The specific ISA you choose matters less than getting started. A £50 monthly standing order into a stocks and shares ISA at age 20, invested in a global index fund, will do more for your financial future than spending six months researching the perfect platform and never opening one.
Open an account. Set up a standing order. Revisit the details once a year. That is the entire strategy for most people in their twenties, and it works.
The Money Sorted Investment Fundamentals course covers choosing platforms, understanding fund types, and building a portfolio in much more detail.
This article is part of the Money Sorted series on moneysorted.money. For more on saving, investing, and building wealth, explore the full range of articles, courses, and eBooks.