Additionally, the portfolio holds assets in government bonds that try to limit the negative effects of inflation, such as iShares Barclays TIPS Bond (NYSEArca: TIP) at 20%, Vanguard Short-Term Bond ETF (NYSEArca: BSV) at 11%, and a smaller allocation in SPDR DB International Government Inflation-Protected Bond (NYSEArca: WIP) at 3%.

Equities holdings include the basic U.S. market-capitalization funds with some international diversification, including the Vanguard Mega Cap 300 Index (NYSEArca: MGC) at 20%, Vanguard Mid-Cap ETF (NYSEArca: VO) at 7%, Vanguard Small-Cap ETF (NYSEArca: VB) at 3%,  iShares MSCI EAFE Index (NYSEArca: EFA) at 7% and the Vanguard Emerging Markets ETF (NYSEArca: VWO) at 1.5%.

Around 6% should be held in cash or cash equivalents. Cash held should be dependent on spending needs, income generating assets and the size of the overall portfolio, according to Morningstar, the Chicago-based investment researcher.

For more information on ETFs for retirement, visit our retirement category.

Max Chen contributed to this article.