We have some exciting news to share! The Motley Fool UK has now become The Twelfth Magpie -- an independent, UK-owned company, led by our long-serving UK management team — Mark Rogers, Chris Nials and Heather Adlington. In practical terms, it’s the same team you know, now fully focused on serving our UK readers and members.

Just as importantly, our approach remains unchanged: long-term, jargon-free, and on your side. This site is our new home, and there will be extra tweaks made across the coming few days as we settle in. So if anything looks a little off, please bear with us!

The content of this article was relevant at the time of publishing. Circumstances change continuously and caution should therefore be exercised when relying upon any content contained within this article.

My simple plan for a £1m ISA with just £250 a month

Do you think you will never be an ISA millionaire? It’s time to think again, says Rupert Hargreaves.

You’re reading a free article with opinions that may differ from The Twelfth Magpie’s Premium Investing Services. Become a member today to get instant access to our top analyst recommendations, in-depth research, investing resources, and more. Learn more, and get a free 'Best Buy Now' stock!.

Making £1m in the stock market might seem like an unrealistic dream but, according to my figures, it’s entirely possible to hit this target in a relatively short period. And you can do so without having to be an investing genius or qualified accountant. So I’m going to explain my simple plan for a £1m nest egg with just £250 a month. 

Tax-free

I believe the best instrument to use if you are going to try and make a million in the stock market is an ISA wrapper. The great thing about ISAs is that any money you make inside this investment wrapper is tax-free. So you don’t have to worry about handing any of your profits over to the taxman — that applies for both income tax and capital gains.

Should you buy Rolls Royce shares today?

Before you decide, please take a moment to review this report first. Despite ongoing uncertainties from US tariffs to global conflicts, Mark Rogers and his team believe many UK shares still trade at substantial discounts, offering savvy investors plenty of potential opportunities to learn about.

That’s why this could be an ideal time to secure this valuable research – Mark’s analysts have scoured the markets to reveal 5 of his favourite long-term ‘Buys’. Please, don’t make any big decisions before seeing them.

You can save a maximum £20,000 a year in an ISA, which easily covers the £250 a month contribution I believe is required to make a million. The best way to invest these funds is, according to my calculations, in a low-cost FTSE 250 tracker fund. Over the past decade, the FTSE 250 has produced an average annual return of around 12.5%.

There’s no guarantee this will continue, but I believe there’s a strong chance over the long term, the index’s average annual return will be in the high-single, to low-double digits. So, for this article, I am going to assume that the FTSE 250 will yield an average annual return of 10% for the foreseeable future.

At this rate of return, I calculate an investment of just £250 a month that increases in line with inflation will be enough to help you make a million within three decades. This is based on the assumption inflation averages 3% per annum during this timeframe, and the monthly contribution is increased at the same rate to keep up with the general rising level of prices. In this example, I’m also assuming the saver starts with a full ISA of £20,000 as a solid base.

Without that base to start saving from, it’s still possible to make a million with £250 a month, it will just take a little longer. Indeed, according to my calculations, it will take over 34 years of saving £250 a month, rising with inflation, at an average annual return of 10% to make that golden number.

The bottom line

So that’s how I plan to make a million in my ISA by saving just £250 a month. As I’ve tried to explain above, you don’t need to be a financial genius to make this return. All you need is a simple, low-cost FTSE 250 tracker fund… and time.

As long as you are saving enough and resist the temptation to tinker with the portfolio, over the long term, your money should look after itself and grow into a sizable pension pot, which will allow you to retire in comfort.

Rupert Hargreaves owns no share mentioned. The Motley Fool UK has no position in any of the shares mentioned. Views expressed on the companies mentioned in this article are those of the writer and therefore may differ from the official recommendations we make in our subscription services such as Share Advisor, Hidden Winners and Pro. Here at The Motley Fool we believe that considering a diverse range of insights makes us better investors.

More on Investing Articles

Engineers in data centre using device, verifying firewall configurations. Teamworking IT professionals performing equipment vulnerability scans in server hub using tablet
Investing Articles

Meet the Legal & General ETF crushing the FTSE 100 index in 2026 

Ben McPoland highlights a thematic ETF that has beaten the FTSE 100 index by a wide margin recently. But is…

Read more »

Rolls-Royce's Pearl 10X engine series
Investing Articles

Here’s what £500 invested in Rolls-Royce shares a year ago is worth now

Christopher Ruane looks at how Rolls-Royce shares have outperformed the market over the past year -- and explains whether he…

Read more »

Investing Articles

Prediction: by August 2027 the BT share price and dividend could turn £9,999 into…

The BT share price has retreated in recent weeks. Now Harvey Jones checks out the FTSE 100 company's income and…

Read more »

Young Asian woman holding a cup of takeaway coffee and folders containing paperwork, on her way into the office
US Stock

£3,846 invested in Micron stock now could be worth this much by summer 2027

Jon Smith makes a call on where he sees Micron stock potentially trading over the coming year and weighs this…

Read more »

UK financial background: share prices and stock graph overlaid on an image of the Union Jack
Investing Articles

Here’s why the Diageo share price is up 10.5% since 1 July

The Diageo share price has outperformed the FTSE 100 this month. But is this yet another false dawn for long-suffering…

Read more »

Warhammer World gathering
Investing Articles

My favourite FTSE 100 stock just got cheaper. Time to consider buying?

Paul Summers checks out the latest set of full-year numbers from this highly-profitable FTSE 100 stock. What's got investors spooked?

Read more »

UK financial background: share prices and stock graph overlaid on an image of the Union Jack
Investing Articles

By mid-2027, £5,000 in this FTSE 250 stock could grow to £8,200, if analysts are right

FTSE 250 stock Raspberry Pi is up almost 50% over the last year. And analysts at Peel Hunt expect the…

Read more »

British flag, Big Ben, Houses of Parliament and British flag composition
Investing Articles

By mid-2027, analysts expect Barclays’ share price to hit…

Barclays’ share price has pulled back after the bank’s H1 results. However, analysts expect it to rise over the next…

Read more »