With the tax filing deadline of April 17 a few days away, investors still have some time to make contributions to their individual retirement accounts (IRAs) for the 2017 tax year.

IRAs allow investors to buy individual stocks, bonds, ETFs or mutual funds.ETFs are becoming increasingly popular with investors due to their low cost, transparency and tax efficiency.

ETFs are excellent tools for retirement investors as well since they provide an easy way to build a diversified portfolio at a low cost. Further, income paying ETFs are better placed in an IRA as income is sheltered from taxes.

Before investing for retirement, investors need to assess their investing goals, time horizon and risk tolerance.

Investors need to remember that performance of an investment portfolio depends mostly on asset allocation, i.e. how an investor allocates money among major asset classes such as stocks, bonds, alternative assets and cash.

Low-cost, broad, diversified funds are more suitable for retirement investors as core, long-term investments rather than costly, narrow-focused or niche ETFs, which should mainly be used as shorter-term tactical trading vehicle.

Expense ratio of an ETF should be an important consideration in retirement investing, as in the long-term, cheaper funds can significantly outperform their more expensive counterparts, other things remaining the same.

Here are some ETFs that are excellent long-term investments for retirement accounts:

iShares Core S&P Total U.S. Stock Market ETF (ITOT – Free Report)

ITOT is a convenient way to get exposure to the entire US stock universe, ranging from some of the smallest to largest companies at an extremely low cost of just 3 basis points.

It holds more than 3,600 stocks in its basket and should be a core holding in any long-term focused portfolio. Apple (AAPL – Free Report) , Microsoft (MSFT – Free Report) and Amazon (AMZN – Free Report) are its top holdings.