ISA Deadline 2026: Don’t Just Use This Year’s Allowance!

With the ISA deadline on 5 April fast approaching, a lot of savers are understandably focused on one thing: using as much of this year’s £20,000 ISA allowance as possible before it disappears.

That makes sense. Once the tax year ends, any unused ISA allowance is gone for good.

But there’s another part of the ISA season story that often gets overlooked — and it could matter just as much as this year’s contribution. If you’ve got old Cash ISAs sitting in accounts opened years ago, there’s a good chance some of that money is now earning far less interest than you think.

In other words, the deadline is not just about adding new money. It’s also one of the best times of year to review your existing ISA savings and ask whether your old accounts are still competitive.

The ISA deadline is important — but it’s not the whole picture

Every tax year, savers can put up to £20,000 into ISAs. For many people, the final days before 5 April are a last-minute push to use whatever allowance they have left.

But concentrating only on new contributions can mean missing the bigger opportunity.

Many savers have far more money in previous years’ ISAs than they are adding right now. If those old balances are stuck in poor-paying accounts, the difference in interest can be significant. Even a gap of 1 or 2 percentage points starts to add up quickly once you are dealing with five-figure balances.

That means the real value of ISA season is often not just opening a new account, but checking whether your old tax-free savings are still working hard enough.

Why old Cash ISAs can quietly become poor value

A Cash ISA might have looked competitive when you first opened it. The problem is that many providers do not keep those rates competitive forever.

Once a bonus expires or a fixed term ends, older ISA accounts can drop onto much lower follow-on rates. Savers who never check again can end up earning far less than they would get by switching to a better deal.

This is where a lot of people lose out. They assume that because the money is already inside an ISA wrapper, everything is fine. The tax-free status is still there — but the interest rate may no longer be doing you any favours.

With the Bank of England base rate at 3.75%, and several Cash ISAs still paying well above 4%, old ISA balances sitting in much weaker accounts deserve a second look.

The “golden window” before and after the tax year end

This time of year is often one of the most competitive periods for ISA rates.

Providers know savers are actively comparing deals in the run-up to the tax year end, and many push harder for new deposits and ISA transfers. That creates a window where both new-money ISA rates and transfer-friendly deals can become more attractive.

For savers, that means two things can be worth doing before 5 April:

First, use any remaining allowance for the current tax year if it makes sense for you.

Second, review any old Cash ISAs and see whether transferring them to a better-paying provider could improve your return.

Best Cash ISA rates currently on DepositScout

If you are looking at the current market, these are some of the standout Cash ISA rates now listed on DepositScout for balances under £1,000:

Trading 212 Cash ISA – 4.68% AER
Flexible ISA, variable rate, instant access, minimum balance £1

Plum Cash ISA – 4.66% AER
Non-flexible ISA, variable rate, instant access, minimum balance £1

Tembo Cash ISA – 4.55% AER
Non-flexible ISA, variable rate, instant access, minimum balance £1

Tandem Fixed Rate Cash ISA – 4.35% AER
Flexible ISA, fixed for 1 year, minimum balance £1

Moneyfarm Cash ISA – 4.31% AER
Flexible ISA, variable rate, instant access, minimum balance £500

Hargreaves Lansdown Cash ISA – 4.30% AER
Variable rate, instant access, minimum balance £1

Moneybox Cash ISA – 4.26% AER
Non-flexible ISA, variable rate, instant access, minimum balance £500

Atom Easy Access Cash ISA – 4.25% AER
Non-flexible ISA, variable rate, instant access, minimum balance £1

For savers who want flexibility, easy-access options remain attractive, especially if you may need the money. For those happy to lock funds away for a set period, fixed-rate deals can still make sense if you want certainty.

Easy access or fixed rate before the deadline?

This depends on what you want your ISA to do.

If you want the freedom to move money, keep contributing, or potentially access savings later, an easy-access Cash ISA may be the better fit. The leading variable deals are still competitive, and for many savers that flexibility is worth having.

If you are comfortable locking money away for a year, a fixed-rate Cash ISA can offer more certainty. That can be useful if you want to remove the risk of future rate cuts affecting your return.

The right choice is not always the highest headline rate. It is the account that matches how you actually plan to use the money.

Don’t withdraw old ISA money if you want to keep the tax benefits

This is one of the most important points for anyone reviewing older ISA balances.

If you want to move an old Cash ISA to a new provider, do not simply withdraw the money and pay it into a new account yourself. That can take the money out of its existing tax-free wrapper and create problems, especially with previous years’ ISA savings.

Instead, use the official ISA transfer process through the new provider.

In most cases, that means opening the new ISA first, checking that transfers in are allowed, and then completing the provider’s transfer form. The new provider will usually contact the old one and move the funds for you.

This keeps the savings inside the ISA system and protects their tax-free status.

Why this matters more than many savers realise

A small gap in rate may not sound dramatic at first. But once you apply it to a larger balance, the cost of doing nothing becomes clearer.

Someone with a meaningful old ISA balance earning a poor follow-on rate could be missing out on hundreds of pounds a year in interest compared with a more competitive deal. Over several years, that becomes a much bigger number.

That is why ISA season is not only about “Have I used this year’s allowance?” It should also be about “Is my existing ISA money still earning a decent rate?”

A useful ISA deadline checklist

Before 5 April, it is worth asking yourself:

• Have I used as much of this year’s £20,000 ISA allowance as I want to?

• Do I have any old Cash ISAs that I have not reviewed in a long time?

• ISA deadline 2026, cash ISA deadline, best cash ISA rates, ISA transfer, old Cash ISA, ISA allowance 2026, 5 April ISA deadline, DepositScout Cash ISA, flexible Cash ISA,Are those old balances earning less than the best rates currently available?

• Does the account I’m considering accept ISA transfers in?

• Am I choosing between easy access and fixed rate based on my actual needs, not just the headline rate?

If you can answer those questions now, you will be in a much better position before the deadline passes.

The bottom line

The ISA deadline on 5 April matters, but it should not be treated as a one-dimensional scramble to put new money somewhere — anywhere — before the clock runs out.

For many savers, the bigger opportunity is hiding in plain sight: old Cash ISA balances that may have been left behind on uncompetitive rates.

A smart ISA move this week could involve using your remaining allowance, reviewing your older accounts, and making sure your tax-free savings are earning a rate that still makes sense in today’s market.

At a time when top Cash ISAs on DepositScout are still paying up to 4.68% AER, leaving old savings in the wrong place could be far more expensive than many people realise.