Thousands of Stocks and Shares ISAs in the UK today contain more than a million pounds. Every one of them started out empty.

Can we emulate those long-term success stories?

Unless we get very lucky, we’d probably need to be able to invest close to the full £20,000 ISA allowance each year to hit millionaire status. But we could reach £1,000 per month in passive income with a fair bit less.

Here’s what counts

It all comes down to three key things:

• How much can we invest each year?
• How long can we leave it there?
• How much can we earn each year?

How much we have is very much an individual thing. I’ve seen people live miserly lives in order to squirrel away as much as possible. And then retire and die without getting the chance to enjoy it.

For me, it’s a balance. I invest as much as I can, but I don’t deprive myself and my family.

Our timescale also depends. How old we are, and what level of final income we need are key. I’ll work on the £1,000-per-month goal and see how long it might take.

Stock market profits

Finally, how much are we likely to make each year?

The FTSE 100 has produced an average annualised return of 6.9% over the past 20 years. What stock might I expect to come close to that in the future? I’ll pick National Grid (LSE: NG.) as an example.

We’re looking at a forecast dividend yield of 4.8% for 2025. And if the shares just keep pace with inflation in the long term, that could bring the total up to around 6.9%.

Balanced ISA picks

The first thing I notice from the chart above is that share prices can be volatile. For me, that means three things.

One, I look for shares paying decent dividends. Dividends are never guaranteed, and they are sometimes cut. But they give me less stress than watching daily share price moves. And the National Grid dividend has a good track record of stability.

Two, I go for diversification, to reduce my overall risk should a stock go bad. There are enough good dividend stocks on the FTSE 100 to make me confident I can achieve my goals over the long term.

Three, I’ve already said it, and I’ll repeat it. Long term, that’s what it’s all about.

What’s it worth?

Using the National Grid example, how soon could I be earning £1,000 a month?

I calculate that investing £500 per month for 20 years should do it. With dividends reinvested, a total annual return of 6.9% could grow that into £252,000. And a 4.8% dividend yield could then pay £12,000 per year.

Or with £1,000 per month I could be looking at a cool half million in that time, generating a £2,000 monthly dividend income.

There’s no guarantee of any of this. And National Grid is just an example, not a recommendation. But buying top quality UK dividend shares and holding for a couple of decades is not just my top personal choice, it’s my only choice.