Just in case you haven’t been swamped by emails from nonprofit groups seeking your Day of Giving dollars, here’s a reminder: The Pittsburgh Foundation’s annual 24-hour matching-fund drive starts at midnight tonight.

The list of more than 700 eligible recipients includes everything from familiar charities to social-service groups, arts organizations, libraries, community groups, and even colleges and universities. (Strangely, no sign of the region’s $10 billion “non-profit,” UPMC.)

It works like this. The Pittsburgh Foundation has $750,000 in funds to divide among all Allegheny County-based recipients. (There’s also a match pool of up to $95,000 for Westmoreland County.)

For every dollar you give to your favorite group during this 24-hour period, PittsburghGives donates a pro-rated portion of its total pool of matching funds. So if, for instance, donors give a total of $8 million to all groups in the county, the match will be 9 cents on the dollar, making each $50 donation worth $54.50.

Admittedly, that match amount has been dropping, but that’s largely a testament to how popular Day of Giving has become.

In 2010, 7,800 donors gave $3.3 million. In 2011, the figures rose to 13,600 donors and $6.4 million. Last year, the Pittsburgh Foundation hoped to top $7 million; instead, says Foundation spokesperson Christopher Whitlatch, some 17,000 donors gave about $8.5 million.

Whitlatch says the Foundation anticipates about $8 million in donations this year. But he notes that the rules have changed a little. Previously, PittsburghGives matched donations up to $10,000 from a single person to an individual group. This year, in hopes of spreading around the largesse, PittsburghGives has limited the match to $1,000 per donor per group. (You can still give as much as you want, of course; it just won’t all be matched.) The minimum gift is $25.

The giving starts at midnight tonight and goes till 11:59:59 p.m. tomorrow; donations will be accepted only during this 24-hour period.

Only MasterCard and Visa donations will be accepted and matched for this event.

The match funding, by the way, is provided by The Pittsburgh Foundation, The Jack G. Buncher Charitable Fund, The Colcom Foundation, The Donald & Sylvia Robinson Family Foundation and The Robert Waters Fund.

The complete instructions and list of organizations are at pittsburghgives.org.