Only 27 amendments have been added to the Constitution in 236 years. The last one passed in 1992—after sitting dormant for 203 years.
Constitutional amendments require two-thirds of both houses of Congress to propose them, then three-fourths of state legislatures to ratify them. That's 290 votes in the House, 67 in the Senate, and 38 state legislatures all saying yes. This supermajority requirement means amendments have more democratic approval than ordinary laws, which makes them nearly impossible to repeal. Congress has considered over 11,000 amendment proposals since 1789. Only 33 made it to the states for ratification.