Legislation signed by President Obama earlier this month permanently enables individuals ages 70 1/2 and older to make a donation of up to $100,000 directly from an IRA to charity. Taxpayers can't get a charitable deduction from this type of donation (called a qualified charitable distribution, or QCD), but effectively they get the same tax break. That's because the QCD amount is subtracted from taxable income.

The new law had been a temporary measure that got extended annually by Congress for years. It lets spouses each donate $100,000 from their individual accounts toward a QCD, for a total of $200,000 a year.

Some quirky rules apply to QCDs. For one, unlike regular charitable donations, QCDs must be in cash. So if you're planning one of these, contact your brokerage immediately to ensure there's still time to liquidate holdings and have the donation count. Here's more to know:

• Donations from cash or money-market accounts. If you're writing a check yourself from your IRA account and sending it directly to the charity, the charity must cash the check before the QCD can be eligible for a tax break. So for a last-minute donation, you'll need to follow up with your brokerage to ensure the check has cleared.

"It's not true that the charity just has to receive the check," says Maura Cassidy, director of retirement products at Fidelity Investments. "The money has to come out of the account by December 31."

• Gifts of less than $10,000 from non-cash investments. Your broker can liquidate holdings and send the money directly to the charity; the donation date is when the check is sent. Cassidy notes that in her company's case, the donation envelopes go directly to a postal facility by the Fidelity campus in Covington, Ky.

• Contributions of $10,000 or more from non-cash investments. Your brokerage firm will have to liquidate the holdings and then mail you a check; you'll then have to post it and get confirmation that the charity has cashed it in time. Unless you've got a personal courier, that might be difficult to do in the next two days.