Cautious investors wonder if they own enough different stocks, or perhaps even too many.

The right number of stocks for investors to own for portfolio diversification depends, in part, on where they are in their investing careers.

When they’re just starting out, most people have modest amounts of money to invest. Even so, it generally pays to invest at least several thousand dollars at a time, or the broker’s minimum commission will significantly lower profits.

For proper portfolio diversification, investors should aim to initially invest in a minimum of four or five stocks — one from each of most, if not all, of the five main economic sectors: Finance, Consumer Goods & Services, Resources & Commodities, Manufacturing & Industry, and Utilities. But they can buy them one at a time, over a period of months or even years, rather than all at once. After that, they can gradually add new names to their portfolios as funds become available, taking care to spread their holdings out as mentioned.

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When an investor’s portfolio gets into the $100,000 to $200,000 range, they should aim for perhaps 15 to 20 stocks. If they’re married, it’s best to treat their family holdings as one big portfolio, even if each spouse keeps their money separate. This way, they can be sure they aren’t operating at cross purposes, or investing too much of the family fortune in a single area.

When investors get above $200,000 or so, they can gradually increase the number of stocks they hold. When their portfolio reaches the $500,000 to $1-million range, 25 to 30 stocks is a good number to aim for to achieve proper portfolio diversification. Of course, they may fall a few stocks below that range, or go a few above it, particularly when they’re making changes in their holdings.

The upper limit for portfolio diversification is around 40 stocks. Any more than that, and even the best choices will have little impact on an investor’s personal wealth.

Whatever the size of your portfolio, be sure to spread your investments across the five main economic sectors. That way, you avoid loading up on stocks that are about to slump simply because of industry conditions or changes in investor fashion. By diversifying across the sectors, you also increase your chances of stumbling upon a market superstar — a stock that does two to three or more times better than the market average. These stocks come along every year. By nature, their appearance is unpredictable; if you could routinely spot them ahead of time, you’d quickly acquire a large proportion of all the money in the world, and nobody ever does that.