At long last, Congress passed meaningful federal estate tax relief at the end of 2010. Among myriad other tax law provisions in the Tax Relief, Unemployment Insurance Reauthorization and Job Creation Act of 2010, there’s a generous $5 million estate tax exemption, and the top estate tax rate has been cut to 35%—the same as the top rate for ordinary income. The law also coordinates other estate tax breaks for wealthy families.

But there’s a downside to these favorable estate law alterations—they’re scheduled to expire after 2012. So there’s only a small window of opportunity before the next crucial crossroads for estate planning, and because it’s impossible to know what will happen next—or to guess what estate rules will be in effect at your death—the positive aspects of the new law could end up having a negative impact. Families whose wealth falls below the higher exemption amount may be lulled into doing nothing, but that’s a risky approach.

It took Congress almost a decade to revisit the subject of estate taxes, and it only finally happened because not acting would have had a dramatic result. In 2001, the estate tax was repealed—but only in a very gradual way, and only temporarily. During the years that followed, the exemption level rose gradually to $3.5 million and the top estate tax rate inched down to 45%. Then, in 2010, the tax was truly gone, but only for a year. Without the 2010 law, passed as the clock wound down on a lame-duck session of Congress, 2011 would have reinstated an exemption of just $1 million and a top tax rate of 55%. Finally, as part of an 11th hour tax compromise brokered by the Obama administration between congressional Republicans and Democrats, the new two-year estate law came into being.

Though the $5 million estate tax exemption and the 35% tax rate have gotten most of the attention, the new law also included other significant changes. The individual exemption is now “portable” between spouses, so that a surviving spouse can utilize any unused portion of a deceased spouse’s exemption. That effectively lets married couples exclude $10 million from estate tax liability—but only if both die before 2013. The new law also again gives heirs a “step-up” in the cost basis of inherited assets—an advantage they didn’t have in 2010—and reunifies the rules for estate and gift taxes so that they share the $5 million exemption. That amount in total can now be transferred from your estate either before or after your death without incurring either kind of tax.

With these changes in effect, estate planning may seem easier than it was before, particularly if you have less than $5 million—or less than $10 million, between you and your spouse—to transfer to your heirs. Doing nothing at all now may seem like a reasonable option. But the biggest problem, again, is that the new rules are guaranteed to hold sway only through the end of 2012. If Congress then reduces the exempt amount—and, in the meantime, your wealth has grown—you might have to scramble to get a new estate plan in place.

What can you do in the meantime? One effective strategy is to continue to take advantage of rules for yearly giving that can reduce the size of your estate. Under the annual gift tax exclusion, you can give anyone assets valued at up to $13,000—$26,000 if your spouse joins in the gift—and you can make such transfers to as many people as you like each year. You can also avoid the issue of future estate tax rates by using your current $5 million credit to transfer additional wealth while you’re alive.

You can also pay attention now to estate issues that have nothing to do with taxes. It’s important to decide how to divide assets among your children, for example, and how to protect your wealth from creditors. Making provisions for the care of a disabled child, perhaps by establishing a special needs trust, could also be crucial. Indeed, trusts of various kinds might help you support your family and philanthropic organizations long into the future, regardless of what happens next to the political football of the estate tax laws.

For now, the latest big changes make this a good time to take stock of your estate plan, making any adjustments that may be needed in terms of how it is structured and in the language of your will and other documents. And, until a long-term law is in place, it’s a good idea to review your estate plan every year or two. We can work with you and your attorney to make sure you’re taking advantage of today’s opportunities.