The deadline for the current Stocks and Shares ISA year is next Sunday (April 5). Given the increased attention on ISAs ahead of the deadline, some might be considering opening one for the first time.

Even though it might seem difficult starting from £0, it’s possible to grow the portfolio to seven figures over time. If I were starting all over again, here’s how I’d go about it.

Patience needed

The maximum someone can invest per ISA year is £20k. Therefore, it’s immediately clear that this process to reach a million will take many years. The key factor that could speed things up isn’t the amount of money available to invest, since it’s capped at £20k a year. Rather, it’s the annual rate of return.

To this end, I’d look to allocate the bulk of my exposure to high-growth stocks. True, these are riskier than buying defensive shares or other sectors, but ultimately I’m looking for growth over the coming decade and beyond. So targeting exciting companies in tech, AI and finance could be the leaders of tomorrow (with a market-cap to match!).

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I can still aim to diversify my ISA by including growth stocks from a variety of sectors, including the ones mentioned above. I’d also diversify by geography, including shares from the US. After all, particularly when it comes to AI, the focus is very much on US-listed companies.

Regarding allocating money to the ISA, I’d aim to contribute £1.66k a month. This eases cash flow pressure versus putting £20k in a lump sum. Based on having most of the money in growth shares, I’d estimate that a 10% rate of return is a fair forecast over the long term. In theory, if I kept this up for 19 years, I’d hit the targeted £1m portfolio value.

Of course, trying to forecast out this far in advance isn’t an exact science. Stocks can rise and fall every day, meaning that the 10% return might not be accurate for all the companies in the ISA.

A firm for the future

One company to consider adding would be CrowdStrike Holdings (NASDAQ:CRWD). The stock’s up 5% in the past year, and has doubled in value over the past five years.

The business focuses on cybersecurity, aiming to stop data breaches using its AI-native platform, Falcon. The platform offers next-gen antivirus and ransomware protection.

I think it could be a great AI growth pick for the next decade, given the expansion of the target market. Every company’s becoming cloud-based and AI-enabled, which means the risk of constant attacks is high. This makes security spending on CrowdStrike products almost non-optional. More than that, the spend should grow as the companies using it grow too.

I also like the fact that it uses a subscription model. This helps create steady, recurring revenue with strong retention rates. Earlier in March, results showed it surpassed £3.73bn in annual recurring revenue, a 24% year-on-year growth rate.

One risk is growing competition. Microsoft and others are making a push in this space, which could hinder CrowdStrike’s long-term growth prospects. Even with this, I still believe it’s a stock to consider for this ISA strategy.