At first glance, figuring out how much you need in an ISA to achieve a desirable passive income seems like a worthwhile endeavour. Take an income target – £25k a year, for example – then reverse-engineer exactly what’s needed to achieve it. Job’s a good ‘un, n’est-ce pas?

Here’s the problem: this strategy resembles very little to the way the average Briton invests. Sure, if you’ve got a million quid laying around then it’s fine (although it”ll take you decades to get that in an ISA given the deposit limits). But for those of us squirrelling away a few quid here and there from the day job, there’s a much more useful way to think about things.

The crazy part

To start with, that £25k passive income can be worked out pretty quickly. Using the popular ‘4% rule’ – which means withdraw 4% of your nest egg each year – then you would need £1m in an ISA. Quite a lot of money. Does that means it’s time for non-millionaires to exit stage left? Definitely not.

With a solid saving strategy and time to let a few good investments work the compound interest, we can get to the same amount. An investor starting with £10k and adding £400 a month for 30 years will end up with a million in an ISA. That’s assuming an average 10% rate of return.

Here’s the crazy part. On that calculation, the total deposits are only £144k but have built up to £1,000k or £1m in the ISA. Following this strategy means the investor has got around seven times more out than what they put in.

A stock for the ISA?

It must be said that there are no guarantees with this type of investing. Stocks can go down as well as up. Entire markets can have long downturns or periods of stagnation too. But there’s also the chance of doing better than the average too. And that’s why some investors might like the sound of a stock like Nvidia (NASDAQ: NVDA).

As the heart and soul of the artificial intelligence (AI) revolution, the American chipmaker needs little introduction. It’s now the largest company in the world. And those who had the foresight to buy in before the AI boom have made out like bandits.

Will Nvidia keep outperforming? Worries about an AI bubble suggest not. If the technology proves less useful than some are suggesting, then the company will be hit harder than most. And even if AI achieves the kind of outrageous productivity gains predicted, much of the value in the share price may already have been baked in.

With all that said, the data from Stocks and Shares ISA show this is a popular stock to hold. It might even be the kind of wealth-building investment that leads to big passive income a few years down the line. I think it’s worth considering.

John Fieldsend has positions in Nvidia. The Twelfth Magpie has recommended Nvidia. 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 and Hidden Winners.