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.

I’d aim to turn a £20k ISA into passive income of £13,959 a year

Let’s say I had no savings and no experience of investing. How would I invest a £20k Stocks and Shares ISA for lifelong passive income? Let’s find out.

Young mixed-race woman jumping for joy in a park with confetti falling around her

Image source: Getty Images

You’re reading a free article with opinions that may differ from The Motley Fool’s Premium Investing Services. Become a Motley Fool member today to get instant access to our top analyst recommendations, in-depth research, investing resources, and more. Learn More.

My first try at passive income failed miserably. I optimistically put a few thousand pounds in the premier savings account of a ‘big 4’ bank. After a month, I got back 40p. 

As irritating as investing at near-zero interest rates was, I learned from the experience. And since then, I’ve discovered better ways to multiply the cash I save from the day job.

XXX

Let’s say I was starting again today with a £20k Stocks and Shares ISA. Here’s how I’d swerve the years of mistakes and target £13,959 of passive income a year.

Opening the ISA itself would be the first hurdle to clear. Investing in stocks would have sounded crazy to me at a younger age. I pictured the stock market as loud trading floors and people dressed like Gordon Gekko – not something I saw myself getting involved with. 

Investing timeline

What changed my mind was comparing the returns to other asset classes. Whether it’s gold, property, savings accounts, or anything else, for smaller investors, the stock market is the best place to make money.

Take a savings account. I could get a guaranteed 5% at the moment. Sounds pretty good? Well, no, I don’t think so. I’ll explain why by looking at how my £20k in a Cash ISA would grow over a 30-year investing timeline. 

5%
Start£20,000
5 years£25,526
10 years£32,578
20 years£53,066
30 years£86,439

Okay, that’s a decent baseline. I’ve made some money. I could even withdraw a small passive income from it too. So what about a Stocks and Shares ISA then?

Well, stocks are more volatile. I couldn’t rely on a regular cash return each year. On average though, a target of 10% is in line with historical averages. Let’s use that for this example.  

10%
Start£20,000
5 years£32,210
10 years£51,875
20 years£134,550
30 years£348,989

Right, what’s going on here? My 5% return gives me £86k and my 10% return gives me £349k. Doubling the rate of return should double the final cash amount, shouldn’t it? Well, no, it actually gives back a lot more cash than anyone might expect. 

It sounds strange at first, but this is simply the unique effect of compound interest. I make much more money because I’m getting ‘interest on the interest’. Even a few percent extra balloons the size of the nest egg. 

Grow wealth

Of course, there are risks here. I’m basing my potential earnings by looking at the past. Historical stock market returns were lucrative. But the future? No one has a crystal ball. 

Also, I wouldn’t withdraw 10% as income. I’d use the 4% rule for withdrawals to ease the impact of volatility. The above example would hand me passive income of £13,959 a year. 

I only compared savings accounts and stocks here, but the calculation rings similarly true for other investments — at least the ones those of us on average salaries have access to.

John Fieldsend has no position in any of the shares 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

Friends and sisters exploring the outdoors together in Cornwall. They are standing with their arms around each other at the coast.
Investing Articles

£503 buys 14 shares in this FTSE 250 stock that returned 23.9% annually for the last 15 years

This FTSE 250 stock has averaged a huge return for 15 years. At today's price, £503 buys 14 shares. But…

Read more »

Black woman using loudspeaker to be heard
Investing Articles

£1,000 buys 25 shares in this FTSE 100 stock that’s returned 29.2% annually for the last 10 years

This FTSE 100 mining stock has returned close to 30% a year for a decade. At 3,995p, £1,000 buys 25…

Read more »

Female student sitting at the steps and using laptop
Investing Articles

Down 47%, is this growth stock finally worth buying in May?

With a £288m order book and a hidden pipeline of defence and nuclear contracts, is this growth stock now too…

Read more »

House models and one with REIT - standing for real estate investment trust - written on it.
Investing Articles

2 REITs yielding 7%+ to consider for passive income in 2026

A REIT backed by the NHS and another backed by Tesco and Sainsbury's with both yielding 7%+. Here's why I'm…

Read more »

Woman riding her old fashioned bicycle along the Beach Esplanade at Aberdeen, Scotland.
Investing Articles

Just 97 shares of this UK dividend stock generate £238 in passive income

A 5.7% yield, £238 in passive income from just 97 shares, and one of the most divisive dividend stocks on…

Read more »

ISA coins
Investing Articles

£10,000 in an ISA generates a second income of…

The London Stock Exchange is home to some of the world's most generous dividends. But how big a second income…

Read more »

Shot of a senior man drinking coffee and looking thoughtfully out of a window
Investing Articles

Expert recommendations: 2 top income stocks yielding 7%+!

With yields of 7.2% and 7.8% respectively, these two income stocks are catching the eyes of institutional analysts. Should investors…

Read more »

Illustration of flames over a black background
Investing Articles

3 top income-focused stocks to buy in May 2026, according to experts

Looking for a stock to buy for income in May 2026? Experts have flagged these three UK dividend shares as…

Read more »