Across the United States, fresh breezes and blooming flowers do little to temper the stress some Americans feel as the April 15 deadline for filing federal tax returns looms before them.

The U.S. federal government imposes a tax on income. It’s based on a tax rate that generally increases as income increases. Individuals may deduct a personal allowance (exemption) and certain personal expenses, including home mortgage interest, state taxes and contributions to charity.

Taxpayers usually self-assess income tax by filing tax returns. April 15 is the deadline for filing federal tax returns for income earned in the previous calendar year. Everyone who earned income must file those forms, including the country’s leaders.

President Obama and the first lady filed their income tax returns jointly and reported adjusted gross income of $477,383. They paid $93,362 in total tax, which represents an effective tax rate of 19.6 percent.

The Obamas reported donating $70,712 — or about 14.8 percent of their adjusted gross income — to 33 different charities. (Download the Obamas’ tax return here.)

Vice President Biden and his wife filed a joint 2014 federal income tax return, reporting an adjusted gross income of $388,844. They paid $90,506 in total federal tax, amounting to an effective tax rate of 23.3 percent. The Bidens contributed $7,380 to charity in 2014. (Download the Bidens’ tax return here.)