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How big does an ISA need to be to generate a £1,000-a-month second income?

Andrew Mackie explores the journey to a second income, from growing an ISA portfolio to turning investments into cash-generating assets.

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£1,000 a month in second income from a Stocks and Shares ISA sounds simple enough. Build a large portfolio, reinvest the dividends, and let compounding do the rest.

In reality, the numbers involved are far less forgiving than many investors expect.

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£1,000 a month works out at £12,000 a year, which implies a portfolio of roughly £300,000 using a typical 4% income assumption.

That immediately sets the scale of the challenge: this isn’t a small side portfolio — it’s a six-figure ISA built over time.

The real driver of second income growth

But the more important point is that this figure is not fixed.

Second income inside a Stocks and Shares ISA is driven by three main variables:

  • time in the market
  • portfolio yield
  • ongoing contributions

Fix any two, and the third becomes the key driver of how quickly the £1,000-a-month target is reached.

This is where small differences in returns start to matter more than most investors realise.

To illustrate this, here’s how different annual returns affect the time needed to reach a £300,000 portfolio, assuming a consistent £750 monthly contribution:

  • At 4% annual return: approximately 21.6 years
  • At 6% annual return: approximately 18.9 years
  • At 8% annual return: approximately 16.9 years
  • At 10% annual return: approximately 15.4 years

Even though the final goal is identical in every case, the journey differs by more than five years depending on returns alone.

Beyond dividend stocks

Many investors focus exclusively on dividend shares when targeting a second income. However, growth stocks can also play an important role in accelerating portfolio growth.

That’s one reason I continue to like Games Workshop (LSE: GAW). The company behind the Warhammer franchise doesn’t offer the eye-catching yields available elsewhere in the FTSE 100, but it has delivered exceptional shareholder returns over many years.

The business recently reported another record performance, with profitable sales growth across all 23 core markets. Management credited strong demand for new miniature releases, growth from existing products, and deeper engagement with the wider Warhammer hobby.

What I find attractive is the combination of growth drivers. The core business is expanding globally through stores, distributors, and online sales.

At the same time, the company generates valuable licensing income from video games, television, and film projects based on its intellectual property.

Importantly, management remains focused on the long term. In its latest update, the company reiterated that its goal is simple: “to do this forever”.

There are risks. The shares trade on a premium valuation, so expectations already sit high. And while licensing offers an exciting growth opportunity, it still contributes relatively little compared to the core miniature business. Any slowdown in hobby spending could therefore weigh on sentiment.

Bottom line

A £1,000-a-month second income won’t be built overnight. But for investors with a long time horizon, I think companies capable of compounding earnings can be every bit as valuable as a high-yield stock.

That’s why Games Workshop remains on my radar. Its dividend yield won’t turn heads, but the business has repeatedly demonstrated an ability to grow profits, cash flow, and shareholder returns over time. When it comes to building a sizeable ISA, I believe that kind of compounding can be worth its weight in gold.

Should you invest £5,000 in Games Workshop Group Plc right now?

When investing expert Mark Rogers and his team have a stock tip, it can pay to listen. After all, the flagship Twelfth Magpie Share Advisor newsletter he has run for nearly a decade has provided thousands of paying members with top stock recommendations from the UK and US markets.

And right now, Mark thinks there are 6 standout stocks that investors should consider buying. Want to see if Games Workshop Group Plc made the list?


Andrew Mackie does not hold any positions in the companies mentioned.

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