How you can become an ISA millionaire in 20 years

Saving £1m by 2039 could be easier than you think. Here’s how you could do it.

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.

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.

You want to retire before you’re too old to have some fun and enjoy your leisure. And you reckon you’ll need a £1m fund to make sure you can live — and spend — comfortably.

£1m sounds like an ambitious target in 20 years, but it could be easier than you think. Here’s what I think you need to do.

Is £1m enough/too much?

Although it sounds a lot, a £1m retirement pot could be a reasonable assumption for many of today’s workers.

Financial advisers use the 4% rule to calculate how much you can withdraw from a savings pot if you want it to last 30 years. If you’ve got £1m, then you should be able to pay yourself £40,000 each year, plus increases for inflation.

Although I’d argue that many people can manage with less, there’s no doubt £1m should fund a long and comfortable retirement.

How much to save each month

With such long-term planning, we can’t be sure exactly what your money will earn each year. But what we can do is rely on long-term average rates of return from the past. Over a 20-year period, there’s a good chance that historical patterns will repeat themselves.

If you want to save £1m in an ISA, then you have three basic choices — cash, bonds or stocks. Here’s how each asset class performed on average between 1899 and 2016:

Asset class

Average annual return 1899 – 2016*

Cash

4.7%

UK government bonds

5.2%

UK stocks

8.9%

*Source: Barclays Equity Gilt Study 2016

As you can see, over long periods, the UK stock market has delivered considerably greater returns than either cash or government bonds.

Using these rates of return as a guide, I’ve done the sums to work out how much you’d need to save each month to reach a million in 20 years:

Asset class

Monthly ISA contribution

Total contribution each year

Cash

£2,519

£30,228

UK government bonds

£2,377

£28,524

UK stocks

£1,517

£18,204

I should stress that these are estimates. No one can tell you with certainty how much you need to save today to have exactly £1m in 20 years’ time. But I do believe these numbers are a realistic guide to how much you’d need to save.

How would this work?

The annual contribution limit is currently £20,000. This is important. As you can see above, only by putting your savings into the stock market can you save enough to reach £1m and stay within the ISA contribution limit.

Although you could save in a taxable stocks and shares account instead, this could leave you liable to big tax bills in the future. In my opinion, the tax-free qualities of an ISA account give long-term investors a huge advantage.

Where should you put your cash?

You could choose to invest in individual stocks, in the hope of picking winners and beating the market. But doing this successfully over 20 years would require a lot of work and some luck.

In my opinion, it makes much more sense to put your cash into a cheap FTSE 100 tracker fund inside an ISA. Use the accumulation option to reinvest all dividends automatically, and setup your monthly payment with a direct debit. Then forget about investing and get on with enjoying life!

Roland Head has no position in any of the shares mentioned. The Motley Fool UK has recommended Barclays. 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

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

Back above 10,000! Is the FTSE 100 index on track again?

The FTSE 100 index has been yo-yoing up and down with the latest news headlines around the oil crisis. Where…

Read more »

Finger clicking a button marked 'Buy' on a keyboard
Investing Articles

Stock market correction: Is there still time to buy UK shares cheap?

Long-term investors can do well to stay calm through stock market corrections, and even crashes, and pick up shares when…

Read more »

Warm summer evening outside waterfront pubs and restaurants at the popular seaside resort town of Weymouth, Dorset.
Investing Articles

2 FTSE 100 blue-chips to consider for a new £20k Stocks and Shares ISA

Ben McPoland highlights a pair of high-quality FTSE 100 stocks that have strong momentum on their side yet are trading…

Read more »

Young Caucasian woman with pink her studying from her laptop screen
Investing Articles

Are depressed Lloyds shares just too tempting to miss now?

Lloyds shares are coming under renewed pressure as conflict in the Middle East threatens the fragile global economic recovery.

Read more »

Female student sitting at the steps and using laptop
Investing Articles

7 FTSE 100 shares that look cheap after the 2026 stock market correction

Falling stock markets often present bargain opportunities. Let's take a look at some of the cheapest FTSE 100 shares at…

Read more »

piggy bank, searching with binoculars
US Stock

Up 59% this year, this S&P 500 stock is smashing the index!

Jon Smith points out a stock from the S&P 500 that's flying right now as part of a transformation plan,…

Read more »

Businessman hand stacking money coins with virtual percentage icons
Investing Articles

Stock market correction: a rare second income opportunity?

Falling share prices are pushing dividend yields higher. That makes it a good time for investors looking for chances to…

Read more »

Finger clicking a button marked 'Buy' on a keyboard
Dividend Shares

I just discovered this REIT with a juicy 9% dividend yield

Jon Smith points out a REIT that just came on his radar due to the high yield, but comes with…

Read more »