ISAs are the most popular savings product in the UK, but they aren’t always the easiest to understand if you aren’t familiar with the ins and outs. 

Some Cash ISAs (including the Chip Cash ISA) are flexible. That means if you take money out, you can put it back in again within the same tax year, without using up any of your annual £20,000 ISA allowance.

But your ‘replaceable ISA allowance’ goes beyond that. 

‍This is the extra "capacity" created when you withdraw money from a previous tax year. Instead of losing that tax-free space forever, you get a temporary window to put that exact amount back in without it counting as a new contribution.


Your Chip Cash ISA is a cash ISA provided by ClearBank Limited. ISA limits apply. Deposit up to £20k per tax year. Chip does not provide tax advice or financial advice. Tax treatment depends on individual circumstances and may be subject to change in the future.

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The previous tax year rules

If you have a large balance built up over several years, a Flexible ISA allows you to treat that "old" money with the same freedom as your current £20,000 allowance.

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You can withdraw "old" money: Let’s say you have £50,000 from previous years, you can withdraw any amount of it, e.g. £30,000, and your "replaceable allowance" for the year effectively becomes £50,000 (£20,000 current limit + £30,000 old money).

‍The "same account" restriction: While you can pay current year replacements into different ISAs, you must pay previous year replacements back into the exact same account they were taken from.

‍The "use it or lose it" deadline: Regardless of how old the money was, the "flexible window" always slams shut on 5 April. If you withdraw £30,000 of old money in August 2025, you have until midnight on 5 April 2026 to replace it. If you miss that date, that £30,000 of "tax-free capacity" is gone forever.

How the flexible money goes back in (the order)

HMRC has a "filling up" order for when you pay money back into a flexible ISA so you always know how its affecting you

1. Replenish previous years first: Your deposits first "fill back up" any money you took out from previous years.
   
   
2. Replenish current year next: Once old money is replaced, your deposits then cover any current-year withdrawals.
   
   
3. New subscriptions last: Only after all withdrawals are replaced do your deposits start counting toward your fresh £20,000 annual limit.

Why it can supercharge your tax-free savings‍

A replaceable ISA allowance gives you flexibility that many people don't realise they have.

In practice, this means you can pay in more than £20,000 in a single year, as long as part of that amount is replacing money you previously took out.

That flexibility makes your ISA a more adaptable tool for real life. You can use it for short-term needs, like a house deposit, home improvements, or a major life event, and still keep your long-term plans intact.

It can also be particularly useful if you have already used your £20,000 allowance for new money elsewhere and did not realise (or forgot) you still had the option to replace earlier withdrawals.

The key is knowing the allowance is there, and making use of it within the same tax year if it fits your situation.

Let’s get going.

Stephen.