ISA Deadline 2026: Use Your £20,000 Allowance Before 5 April or Lose It

The clock is ticking. You have until 5 April 2026 to use your full £20,000 ISA allowance for the 2025/26 tax year. Any allowance you don’t use is gone forever — it doesn’t roll over. With cash ISA rates still above 4% AER, there’s never been a better time to lock in tax-free returns before the deadline passes.

Why the ISA Deadline Matters

Every UK adult gets a £20,000 ISA allowance each tax year, running from 6 April to 5 April. Any money you put into an ISA grows completely tax-free — no income tax on interest, no capital gains tax on growth. But here’s the catch: if you don’t use your allowance by 5 April, you lose it. You can’t carry it forward or double up next year.

This year’s deadline is even more important because from April 2027, the ISA allowance is dropping to £12,000 for most people (only over-65s will keep the £20,000 limit). That means the 2025/26 tax year is one of your last chances to shelter the full £20,000.

Best Cash ISA Rates Right Now (March 2026)

Cash ISA rates remain competitive despite the Bank of England’s rate cuts over the past 18 months. Here are the top picks as of 10 March 2026:

• Easy access: Up to 4.61% AER (eToro), 4.56% AER (Trading 212), 4.55% AER (Plum)
• 1-year fixed: Up to 4.30% AER from leading providers
• 2-year fixed: Up to 4.16% AER for those happy to lock away

If you deposited the full £20,000 into a 4.5% easy-access cash ISA today, you’d earn roughly £900 in tax-free interest over the next year. In a standard savings account, a higher-rate taxpayer would lose £360 of that to HMRC.

What About Stocks and Shares ISAs?

If you won’t need the money for at least 5 years, a stocks and shares ISA could deliver higher long-term returns. You can split your £20,000 allowance between a cash ISA and a stocks and shares ISA however you like. Many investors put emergency funds in a cash ISA and longer-term savings into investments.

How to Use Your ISA Allowance Before 5 April

1. Check what you’ve already used. Log into any existing ISA providers and check your deposits for this tax year.
2. Compare rates. Use comparison sites to find the best cash ISA or stocks and shares ISA for your needs.
3. Open and fund your ISA. Most providers let you open an ISA online in under 10 minutes. Fund it by bank transfer for the fastest processing.
4. Don’t leave it until 5 April. Applications can take a few days to process, and providers get swamped at deadline time. Aim to have everything done by 1 April at the latest.

Key Things to Remember

• You can only pay into one cash ISA per tax year (though you can transfer old ones freely)
• The £20,000 limit covers all ISA types combined — cash, stocks and shares, innovative finance, and Lifetime ISAs
• Transferring between ISA providers doesn’t use any new allowance
• From April 2027, the allowance drops to £12,000 — so maximise while you can

The Bottom Line

With less than four weeks until the ISA deadline and a major allowance cut on the horizon, now is the time to act. Even if you can’t use the full £20,000, putting whatever you can into an ISA before 5 April means tax-free returns that compound year after year. Don’t let your allowance go to waste.

You Might Also Like

• Best Cash ISA Rates UK 2026
• ISA Allowance Dropping to £12,000 From April 2027
• How to Make the Most of Your £20,000 ISA Allowance