In your 30s, you're at a critical juncture in your wealth-building journey. You can get serious about investing, or you can be casual and uncommitted. The serious 30-something investor has a good shot at building wealth momentum and eventually achieving financial independence. The uncommitted investor may be struggling to catch up in 20 or 30 years.

Hopefully, the serious path sounds like the better choice. Get yourself going in the right direction by avoiding these three investing mistakes in your 30s.

1. Not investing at all

Between ages 30 and 61, an invested portfolio could increase in value by 800%. Waiting a decade to invest cuts your growth prospects in half.

Smiling adult couple looks at laptop together.

Image source: Getty Images.

The 800% comes from the rule of 72, which estimates how long it takes to double your money with compound earnings. To use the rule, you divide 72 by your expected annual growth rate. Dividing 72 by an average annual investment return of 7% after inflation gives you an estimated doubling time of about 10 years and four months. The 7% number is the long-term average annual growth of the stock market and a realistic assumption for an equity-heavy portfolio.

The table below shows how the 800% increase applies to a starting value of $10,000 on your 30th birthday.

Balance

Your Age

$10,000

30

$20,000

40 and 4 months

$40,000

50 and 8 months

$80,000

61

Data source: Author calculations.

If you wait until you're 40 to start investing, you miss out on that first doubling cycle. By the time you reach 61, you'll have only doubled your money twice, which grows your $10,000 in this example to $40,000 instead of $80,000.

2. Investing too conservatively

If you want to take calculated risks in your portfolio, the time to do that is now. Riskier stocks have higher growth potential, but they're also more volatile. That's the reason many older investors avoid high-growth stocks. Those investors are, or soon will be, taking retirement distributions. As such, they're reliant on selling stocks regularly to fund their withdrawals. Volatility increases the chances the investor will have to sell when share prices are down temporarily.

Assuming you have a paycheck to cover your bills and some cash savings for emergencies, you shouldn't need to withdraw your invested funds anytime soon. And that means you can invest in growth stocks -- and stay invested -- through any short-term market turbulence. Doing so greatly improves your earnings potential.

The stock market may swing up and down from one year to the next, but longer time frames are more likely to average out to positive returns. Historically speaking, the S&P 500 has rarely lost value over any 10-year period, and it has never lost value over 15 years or more. That's not a guarantee for the future, but it does underscore the point -- having time to stay invested is a luxury you can use to your advantage.

In this window of opportunity, consider investing in growth-oriented positions that might be too aggressive for you later in life. Small-cap and mid-cap funds, recent IPOs, and exposure to emerging markets are just a few examples.

3. Following the tide

Your 30s is the decade to make some financial headway with the goal of coasting into more conservative investing later. Sadly, that plan can get derailed quickly if you make trading decisions based on what everyone else is doing.

Share prices rise when investors are buying confidently and fall when investors are selling in a panic. If you follow those tides, you'll end up buying high and selling low. That strategy isn't profitable, and it will lower your long-term returns. Most of the time, you're better off doing nothing. If you have the fortitude, you could even do the opposite during a downturn, for example, and buy when others are selling off their holdings in a panic. That is the time you're likely to see the best bargains on high-quality stocks.

Setting the stage for future wealth

The investing you do in your 30s should earn set the stage for the capital that you eventually double or quadruple in the decades ahead. Make the most of that opportunity by investing early and often. And to the extent you can handle the risk, look to add growth potential to your portfolio. Just remember that when the market takes an inevitable turn, you must stick to your plan -- no matter what everyone else is doing.

Those simple habits set the stage for future wealth and should prevent you from playing catch-up down the road.