Here’s the one rule that matters: never withdraw the money yourself. If you take cash out of an ISA to move it, it stops being ISA money the moment it leaves — and you can only put £20,000 a year back in. Use the official transfer process instead and everything moves with its tax wrapper intact, however much you’ve built up over the years.
Everything else is detail. Here’s the detail.
What are the exact steps?
Open a Stocks & Shares ISA with an investment platform. This takes about fifteen minutes online.
Fill in their ISA transfer form. You’ll need your Cash ISA provider’s name and your account number. You’re telling the new provider to go and fetch the money.
Choose how much to move. It doesn’t have to be everything — partial transfers are fine, and money from previous tax years doesn’t touch this year’s £20,000 allowance at all.
Wait. The new provider does the chasing. Cash-to-investment transfers are expected to complete within 30 days; most are quicker.
Invest it when it lands. This is the step people miss — the money arrives as cash inside your new ISA, and it stays cash until you buy something. A single low-cost index fund is where I’d start.
That’s the whole process. One form, one wait, one purchase.
Will I lose interest or pay a penalty?
If your Cash ISA is easy-access: no. If it’s a fixed-rate deal, transferring before the term ends usually costs an interest penalty — a few months’ worth is typical. Check your terms; it’s often still worth paying, but know the number first.
Why bother moving it at all?
Because for money you won’t need for years, cash and shares are different machines. A Cash ISA keeps money safe. It does not grow it — that’s the quiet trap.
Take £20,000 sitting in a Cash ISA at 4%. In twenty years it becomes about £43,800. The same £20,000 in a broad index fund averaging the market’s long-run 10% a year becomes about £134,550 — a bumpy ride, but that’s the historical average.
The difference is £90,728. The form takes ten minutes. The difference is ninety grand.
Does the Cash ISA cut change this?
It sharpens it. From April 2027, under-65s can only put £12,000 a year into a Cash ISA — the rest of the £20,000 allowance has to go into investments if you want to use it. The government is pushing savers in this direction anyway. The transfer just gets you there on your own terms, with money you already have.
Keep what you’ll need in the next year or two in cash. Move the rest. That’s not bravery — it’s just putting each pound in the machine built for its job.
This is what I write about every week — managing your own money in plain English, without paying someone 1.5% a year to do it worse. The letter is free.
I am not a financial adviser. Nothing here is personal financial advice. This is my own experience and opinion, shared for information and education. Investing involves risk — the value of investments can fall as well as rise, and you may get back less than you put in. Please do your own research before acting.