U.S. donors gave $3.6 billion on Tuesday, an increase from the past two years, according to estimates from the nonprofit GivingTuesday.

Melinda French Gates is offering to match up to $1 million in gifts to two nonprofit organizations to help spur donations on GivingTuesday.

Some $3.1 billion was donated to charitable causes in the U.S. in the 24 hours that are called Giving Tuesday.

The Bill & Melinda Gates Foundation donated $10 million to the organization that grew out of the hashtag #GivingTuesday in part to fund a database of charitable giving and other acts of generosity.