How big is the UK ISA market in 2026?

HMRC and AJ Bell data published in September 2026 puts the total UK ISA market at £951.9 billion. That covers every type of ISA held by UK adults: cash ISAs, stocks and shares ISAs, Lifetime ISAs, Junior ISAs, and closed Help to Buy ISAs still in drawdown. We are within roughly £50 billion of the £1 trillion round number, which the market is likely to cross by mid-2027 on current growth.

Is £951.9 billion the money UK adults have put in, or the current value?

It is the current market value of the holdings, including the growth on the original subscriptions. The total amount ever subscribed into ISAs is lower, because the figures include the compounded growth on cash interest and on stocks and shares over the life of each account. The £95.6 billion cash ISA and £37.2 billion stocks and shares ISA figures in the September 2026 data are the year-to-date inflows (new subscriptions) for 2026/27, not the total holdings.

How much are people putting into ISAs each year?

For 2026/27 so far, the year-to-date inflows are £95.6 billion into cash ISAs (up 37.5% on the prior year) and £37.2 billion into stocks and shares ISAs (up 19.6%). The cash ISA jump reflects attractive cash ISA rates and a move of higher-rate savers out of standard savings accounts to protect their Personal Savings Allowance. The S&S ISA figure is more measured because a small number of large regular savers account for a meaningful share of the total.

What percentage of UK adults hold an ISA?

About 40% of UK adults hold some form of ISA. That number has been roughly flat for several years. The 60% who do not hold an ISA either keep their savings in current accounts and easy-access pots, or have not engaged with ISAs at all. If you are reading this and you do not have an ISA open, you are in the larger group. The ISA allowance is one of the most generous tax breaks in UK personal finance, and opening one is the first step to using it.

What is the average UK ISA balance?

The Office for National Statistics Wealth and Assets Survey publishes median and mean ISA balances by age band. The median is the more useful figure for benchmarking. Median ISA balances sit around £3,000 for 25 to 34 year olds, around £11,000 for 35 to 44 year olds, around £24,000 for 45 to 54 year olds, and around £46,000 for 55 to 64 year olds. The mean is higher because it is dragged up by a small number of much larger balances.

Should I put money into a cash ISA or a stocks and shares ISA this year?

It depends on when you will need the money and what tax band you are in. Cash ISAs are the right answer for money you might need within three to five years, and for higher-rate taxpayers whose Personal Savings Allowance has run out. Stocks and shares ISAs are the right answer for money you will not need for at least five to ten years, because longer holding periods let the underlying investments recover from any short-term falls. The full split is on the best ISA strategy for 2026/27 page.

How does the 2026/27 ISA allowance work?

Each UK adult under 65 can subscribe up to £20,000 across their ISAs in the 2026/27 tax year, which runs from 6 April 2026 to 5 April 2027. You can split the £20,000 between cash ISAs, stocks and shares ISAs, a Lifetime ISA (capped at £4,000 of the £20,000), and any other ISA type, in whatever combination suits you. From 6 April 2027 the cash ISA allowance halves to £12,000 for under-65s, so this is the last tax year on the old £20,000 cash ISA terms.

What happens to my ISA if I do not use the full allowance?

The unused portion is lost. The 2026/27 allowance of up to £20,000 expires at midnight on 5 April 2027. Anything you do not subscribe by that date disappears. You cannot carry ISA allowance across tax years. The same is true for the Lifetime ISA bonus, which is paid on contributions made before 5 April each year. This is why the second half of the tax year is when most households should be topping up if they have spare cash.

Educational use only. Not financial, investment, tax or legal advice.

29 September 2026 Syd Lawrence 6 min read

The UK Now Has £1 Trillion in ISAs. Here Is Where It All Is.

HMRC and AJ Bell data for September 2026. £951.9 billion held. £95.6 billion of new cash ISA subscriptions this year. 40% of UK adults hold one. Where you probably sit, and the one thing to do before 5 April 2027.

Syd Lawrence

CEO & Co-founder at Delphina

Syd got fed up with being kept confused by the UK personal finance industry. So he built the tool he wished existed. Qualified to provide financial advice, prefers to provide financial clarity. No agenda. Just someone who finally got clear and wanted everyone else to be able to too.

You opened your banking app at 9pm. You scrolled past the balance and closed it. You are not sure whether your ISA is normal.

The UK crossed a quiet threshold this year. HMRC and AJ Bell data for September 2026 puts the total ISA market at £951.9 billion. We are about six months from £1 trillion. This page gives you the breakdown, the benchmarks, and the one thing to check before the 2026/27 allowance disappears on 5 April 2027.

You know the ISA exists. You may even have one open from somewhere you cannot quite remember, with a balance you have not looked at in a year. You have not been ignoring it on purpose. There has just been nothing to do about it that you could feel certain of.

That is the honest reason most people in their late thirties and forties land on this kind of page at night. They are not really searching for the national figure. They are searching for the specific number, the one their own statement should be compared against, that would let them stop guessing.

The data below gives you the comparison. It will not tell you whether your number is good. It will tell you whether you are normal. Whether normal is enough is a different question, and one only your own scenario can answer.

The £951.9 billion, in one table

HMRC publishes the aggregate ISA statistics every quarter. AJ Bell publishes the flow data on subscriptions each month. The September 2026 read across both sources looks like this.

Measure	September 2026	Year-on-year
Total ISA market (holdings)	£951.9bn	Up
Cash ISA inflows (year to date)	£95.6bn	+37.5%
Stocks and shares ISA inflows (year to date)	£37.2bn	+19.6%
S&S ISA accounts contributing this year	4.9m	Up
UK adults who hold an ISA	about 40%	Roughly flat

Sources: HMRC ISA statistics to end-August 2026 (published September 2026) and AJ Bell monthly ISA inflow data, September 2026. Figures rounded. The total ISA market includes cash, stocks and shares, Lifetime, Junior, and Help to Buy ISAs.

The cash ISA figure is the one that catches most people off guard. £95.6 billion of new money going into cash ISAs in twelve months is a 37.5% jump on the prior year. It reflects two things: the better cash ISA rates available since base rate rose, and a chunk of savers moving from ordinary savings accounts into the wrapper to protect their Personal Savings Allowance. The PSA trap page shows why that move makes sense once a pot crosses roughly £15,000 for a higher-rate taxpayer.

What the 40% figure is really telling you

About 40% of UK adults hold an ISA. That means about 60% do not. If you are reading this and you do not have an ISA open, you are in the larger group. That is not a verdict on whether you should have one. It is just useful context before deciding.

The people in the 40% tend to fall into three groups. The first is older savers who built up cash ISA balances in the early 2000s when the rules were different. The second is investors who use a stocks and shares ISA and forget it exists because they set up a monthly direct debit five years ago. The third is younger workers in their first few years of earning above the personal allowance, who have moved savings into ISAs early in their career on purpose.

The people in the 60% tend to fall into two groups. Either they keep everything in a current account or an easy-access pot, or they have never heard of an ISA at all. The first group is leaving tax-free growth on the table once balances grow above the Personal Savings Allowance. The second group typically finds out about the ISA around their first pay rise, their first mortgage, or the first time they search this question at night.

Where the £1 trillion actually sits

The £951.9bn is split across several ISA types. Cash ISAs account for the largest share by far, partly because UK households have been adding to cash ISAs at well above their long-term average. Stocks and shares ISAs hold the second largest share, although inflows to S&S ISAs (£37.2bn) are running at less than half the rate of cash ISA inflows (£95.6bn) this year.

Lifetime ISAs (for first home purchases and retirement at 60) and Junior ISAs (for children) are smaller by comparison but growing. Help to Buy ISAs are now closed to new savers but still hold material balances that need to be used or transferred by 30 November 2029.

The split matters because each ISA type has different contribution limits, different tax treatment on the way in and out, and different rules about when the money becomes accessible. The total figure hides the fact that the right split for you depends on your age, your tax band, and whether you are saving for a first home, retirement, or general long-term wealth.

Holding any ISA at all puts you ahead of about 60% of UK adults

The 40% who hold ISAs collectively hold £951.9bn. The 60% who do not hold ISAs hold that £0 of ISA wealth. The median ISA holder holds a balance in the low five figures. If yours is below that, you are below the middle. If yours is above, you are above the middle. The median is not the test for whether your number is enough. It is the test for whether you are normal.

The £20,000 annual allowance and the deadline

Each UK adult under 65 can pay up to £20,000 a year into a combination of ISAs. The allowance resets on 6 April 2027. Anything you do not use by 5 April 2027 is gone for good.

From 6 April 2027 the rules change. The cash ISA allowance for under-65s halves to £12,000. Stocks and shares ISAs will carry a 22% charge on cash held inside the wrapper that is not invested. S&S to cash ISA transfers will be blocked. The full mechanics are on the budget ISA changes page.

The implication is that whatever you put in your ISA this tax year, you should think of it as the last year on the old terms. After 5 April 2027 the cash ISA becomes less generous for under-65s, and the S&S ISA becomes a wrapper that charges you for the privilege of holding cash inside it. The six-month window from now to 5 April 2027 is the moment to decide how much you want to commit on the old terms.

The one thing to do before the end of October

You do not need to make a £20,000 decision this month. You need to make three smaller ones.

1. Find your current ISA balance

Log in to your ISA provider. Note the total ISA balance across every ISA you hold. Write the number down next to today's date. This is the starting number for the rest of the decisions this year.

2. Decide how much of the £20,000 you will use this year

£20,000 is the ceiling. £100 a month is the floor. The right number is the one you can sustain without dipping into the emergency fund. The best ISA strategy for 2026/27 covers how to split it between cash and S&S.

3. Set the standing order before 31 October

Once you know the monthly number, set up the standing order so it runs automatically. Manual transfers get skipped when life gets busy. The 6-month window between now and 5 April 2027 gives you roughly 26 weekly transfers or 6 monthly ones. Setting it up this week is the action that closes the gap before the deadline.

How you compare to the benchmarks

The benchmarks that matter most for someone in their late thirties and forties are not the £951.9bn national figure or the £95.6bn cash ISA inflow. They are the figures for your age band from the Office for National Statistics Wealth and Assets Survey. Median ISA balances for UK adults sit roughly as follows.

Age band	Median ISA balance (ONS)	What that means
25 to 34	about £3,000	Mostly small cash ISA balances from a few years of saving
35 to 44	about £11,000	The first meaningful ISA pot for most households
45 to 54	about £24,000	Often a mix of cash ISA and S&S ISA from years of allowance use
55 to 64	about £46,000	The ISA pot is now a meaningful part of the retirement picture

Source: Office for National Statistics, Wealth and Assets Survey. Figures rounded. Includes cash ISA, stocks and shares ISA, and Junior ISA held in the adult's name.

The full age-by-age picture is on the average UK savings by age page, which goes broader than just ISAs. The wider am I on track financially page covers the four indicators that matter alongside the ISA balance: pension contributions, mortgage paydown, net worth and an emergency fund.

The ISA figure is one input. The right answer about whether your money is doing what it should comes from your full scenario, with the ISA, the pension, the mortgage and any other investments modelled together. The net worth statement page shows the format for putting all four numbers in one place.

Editorial commentary based on HMRC and AJ Bell ISA market data published September 2026. Not personal financial advice. Verify current rates and allowance rules before acting.