Millennials: What Your Retirement Would Look Like If You Started Investing $100 a Week Today

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It might be hard to believe, but the youngest millennials will turn 30 years old in 2026 and the oldest will turn 45. This means a large portion of millennials are moving into life stages when saving for retirement takes on added urgency.

Many have fallen behind, which makes it even more important to focus on retirement savings and investments.

One thing that stands out is how big a difference your age makes. The earlier you begin investing, the more you benefit from the compounding effect.

Here’s a look at what your retirement would look like at age 70 if you started investing $100 a week today, based on different ages that apply to millennials.

How Much Millennials Make

Millennials have an average 401(k) balance of $67,300 and an average IRA balance of $25,109, according to a March 2025 report from Fidelity. Here’s a breakdown of 401(k) savings for different age groups:

• 30-34: $45,700
• 35-39: $73,200
• 40-44: $109,100

Those balances lag behind Fidelity’s own retirement savings guidelines, which recommend saving 1x your salary by age 30, 3x by age 40 and 6x by age 50.

The median earnings for full-time workers were $1,214 a week, or $63,128 a year, as of the third quarter of 2025, according to the U.S. Bureau of Labor Statistics. Based on that figure, the typical American should have about $63,000 saved by age 30, $94,500 by age 35 and $189,000 by age 40.

The good news is, it’s never too late to start investing for retirement. Depending on how old you are, you could amass nearly $3 million by age 70 just by investing in an S&P 500 fund.

If You Start Saving at Age 29

If you were to make an initial investment of $100 into an S&P 500 fund and then invested $400 a month — roughly $100 a week — until age 70, your final balance would be about $2.8 million.

That’s according to the Troutwood S&P 500 investment calculator and is based on historical S&P 500 returns of about 10% a year. A ChatGPT calculator came up with the same total $2,805,476.

Here’s a breakdown of scenarios assuming a balanced portfolio of 60% stocks and 40% bonds, with $100 invested each week until age 70, based on ChatGPT calculations:

• Total contributions: $213,200
• 7% annual return: $1.03 million final balance
• 6% annual return: $885,000
• 5% annual return: $762,000

If You Start Saving at Age 33

If you were to make an initial investment of $100 into an S&P 500 fund at age 33 and then invested $400 a month until age 70, your final balance would be about $1.87 million, based on historical returns.

Here are the balanced portfolio scenarios:

• Total contributions: $192,400
• 7% annual return: $915,000 final balance
• 6% annual return: $711,000
• 5% annual return: $558,000

If You Start Saving at Age 37

If you were to make an initial investment of $100 into an S&P 500 fund at age 37 and then invested $400 a month until age 70, your final balance would be about $1.24 million, based on historical returns.

Here are the balanced portfolio scenarios:

• Total contributions: $171,600
• 7% annual return: $674,000 final balance
• 6% annual return: $543,000
• 5% annual return: $440,000

If You Start Saving at Age 41

If you were to make an initial investment of $100 into an S&P 500 fund at age 41 and then invested $400 a month until age 70, your final balance would be about $815,735, based on historical returns.

Here are the balanced portfolio scenarios:

• Total contributions: $150,800
• 7% annual return: $480,000 final balance
• 6% annual return: $387,000
• 5% annual return: $313,000

If You Start Saving at Age 45

If you were to make an initial investment of $100 into an S&P 500 fund at age 45 and then invested $400 a month until age 70, your final balance would be about $531,600, based on historical returns.

Here are the balanced portfolio scenarios:

• Total contributions: $130,100
• 7% annual return: $325,000 final balance
• 6% annual return: $265,000
• 5% annual return: $215,000

This article is for informational purposes only and does not constitute financial advice. Investing involves risk, including the possible loss of principal. Always consider your individual circumstances and consult with a qualified financial advisor before making investment decisions.

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