20 Days Left: How to Split Your £20,000 ISA Allowance Before 5 April

The 2025/26 ISA allowance is £20,000, unchanged since 2017. You can split this across a Cash ISA, Stocks & Shares ISA, Innovative Finance ISA, and Lifetime ISA (max £4,000 of the £20,000) in any combination.

Here's what most people miss: unused allowance doesn't roll over. If you shelter £5,000 this year, you haven't "saved" £15,000 for next year — you've lost it. Over a decade, that's £150,000 of tax-free capacity gone. The HMRC guidance on ISAs is clear: each tax year's allowance is use-it-or-lose-it.

At the current Bank of England base rate of 3.75%, even a cautious saver parking £20,000 in a Cash ISA at 4.68% earns £936 per year completely tax-free. A higher-rate taxpayer keeping that same money in a standard savings account would pay £174 in tax on the interest above their £500 PSA. Over 10 years, compounded, the tax drag adds up to over £2,000.

The Personal Savings Allowance gives basic-rate taxpayers £1,000 of tax-free savings interest per year, but higher-rate taxpayers get just £500, and additional-rate taxpayers get nothing. With savings rates at multi-year highs, these allowances are easier to breach than ever. The ISA is the permanent fix.

If you earn above £50,270 and have the full £20,000 to deploy, here's the split I'd use:

£4,000 into a Lifetime ISA — if you're under 40 and buying your first home (worth up to £450,000) or saving for retirement. The government's 25% bonus adds £1,000 free money per year. No other tax wrapper matches this return. If you already own a home or you're over 40, skip this and reallocate to the other pots.

£6,000-£10,000 into a Cash ISA — this is your liquidity buffer. The best easy-access Cash ISAs pay around 4.68% tax-free, significantly above the NS&I Direct ISA at just 3.50%. Moneybox, Chip, and Trading 212 consistently beat the government's own offering. For higher-rate taxpayers, every pound in a Cash ISA avoids 40% tax on interest — that's an immediate 40% boost to your effective return compared to a standard savings account.

£6,000-£10,000 into a Stocks & Shares ISA — for money you won't touch for 5+ years. A global index tracker inside an ISA compounds free of capital gains tax and dividend tax. According to HMRC's current rates, the CGT annual exempt amount is just £3,000 for 2025/26 — down from £12,300 three years ago. The ISA shelter has never been more valuable for equity investors. See our guide to the best S&S ISA providers for platform comparisons, or our investing hub for broader portfolio strategy.

"I get £1,000 tax-free interest through my PSA — why bother with a Cash ISA?" This is the most common objection, and it's dangerously short-sighted.

At 4.68%, £21,400 in savings breaches the basic-rate Personal Savings Allowance. If you have an emergency fund, a house deposit fund, and any other cash, you're probably already there or heading there fast. And the moment you get a pay rise that pushes you into the higher-rate band (above £50,270 in 2025/26), your PSA halves to £500.

The ISA locks in tax-free status forever. Money that enters the wrapper stays tax-free regardless of future rate changes, income changes, or government policy shifts. Think of it as tax insurance — cheap when you don't need it, invaluable when you do. The frozen income tax thresholds until 2028 mean more people are being dragged into higher tax bands each year through fiscal drag. Protecting your savings from this creeping tax burden costs nothing.

For our comprehensive ISA guide covering all four ISA types, contribution rules, and transfer mechanics, start there if this is your first time. If you're deciding between cash and equities, our Cash vs Invest decision framework walks through the key considerations.

Opening a Cash ISA takes 10 minutes online. Opening a Stocks & Shares ISA and actually investing the money takes longer — platforms need to verify your identity, link your bank account, and process the transfer. Budget 3-5 working days.

Critical deadlines:

• 28 March: Last safe date to open a new S&S ISA and have funds invested before 5 April
• 2 April: Last safe date for Cash ISA deposits (some providers need 1-2 business days to process)
• 5 April: Hard deadline. No extensions, no exceptions

If you already hold ISAs from previous years, topping up is faster — log in, transfer funds, done. ISA transfers between providers don't count against your annual allowance, so consolidating old ISAs is always worth doing. The FCA's guidance on ISA transfers confirms providers must process transfer requests within specified timeframes.

One trap to avoid: withdrawing money from a non-flexible ISA and redepositing it. That uses up your allowance twice. Check whether your provider offers flexible ISA terms — if they do, you can withdraw and replace within the same tax year without penalty. This matters most for people who use their ISA as an emergency buffer and might need temporary access to the funds.

Most people don't have £20,000 spare. The median UK household has around £11,000 in savings. Whatever you can shelter, shelter it.

£100 per month into a Cash ISA is £1,200 per year tax-free. £250 per month into a S&S ISA is £3,000 per year sheltered from CGT. The allowance isn't all-or-nothing — partial use still beats no use. Our savings hub has rate comparison tools to find the best Cash ISA for regular contributions.

If you're choosing between an ISA and paying off debt, the debt wins if the interest rate exceeds your ISA return. Credit card debt at 22% APR versus a 4.68% Cash ISA? Pay the card. But a 0% balance transfer? Fill the ISA first and let the interest work for you. The MoneyHelper debt advice service can help you prioritise if you're managing multiple debts alongside savings goals.

For parents, don't forget the Junior ISA — a separate £9,000 annual allowance for under-18s, completely independent of your own £20,000 limit. A family with two parents and two children has access to £58,000 of annual ISA capacity.

This article is for informational purposes only and does not constitute financial advice. You should seek independent financial advice before making any investment decisions.