How much do you need to save each month to get to a million dollars? CNBC crunched the numbers based on these assumptions:

• Starting with no savings.
• Investments earn 6% annually.
• Plan to retire at 67.

That is: You’ll need to save $319 starting at the age of 20 to reach $1 million by the time you retire at 67.

What about investments that return over 6% annually? Can’t go wrong with exchange-traded funds (ETFs)…

The classic: A trusty ETF tracking the S&P 500, an index of 500 of the largest US companies.

• ETF: iShares Core S&P 500 ETF (NYSE:IVV)
• Average annual return since inception (May 15, 2000): 7.27%

The reacher: Betting on technology certainly hasn’t disappointed in the past decade. One of the safer bets is an ETF tracking the NASDAQ 100, an index of the 100 largest US tech-heavy companies.

• ETF: Invesco QQQ (NASDAQ:QQQ)
• Average annual return since inception (Mar 10, 1999): 10.26%

An investment in the QQQ would have given investors a better return but it’s also seen greater volatility during market turbulence.

Both of these ETFs have proven to be resilient investments over the past 20 years, making for great additions to long-term portfolios.