Investors have less than a week to take full advantage of a key tax benefit in opportunity zone funds. They can avoid taxes on 15% of previous capital gains invested in an opportunity zone fund held for seven years only if they make that investment by Dec. 31. The reason: The deferred taxes come due by Dec. 31, 2026.

After Jan. 1, 2020, investors will be eligible for a tax cut of only 10% on those gains so long as they hold the investment for more than five years. These cuts are essentially a step-up in the tax basis of those previous gains.

Tax cuts on previous capital gains are just one benefit of opportunity zone funds. The other is the tax cut on gains made from investments in opportunity zone funds themselves. If those investments are held for at least 10 years, their basis moves up to fair market value when they are  sold or exchanged, which essentially eliminates any capital gains tax on the investment.