Congress cannot amend the US Constitution on its own authority. A 2/3 vote by both houses may authorize that a proposed amendment be sent to the states for ratification. If 3/4 of the states ratify the amendment it becomes effective.
2/3
Two-thirds
2/3
2/3
two-thirds
Three-fourths of state legislatures must approve an amendment proposed by Congress to the United States Constitution. An alternate method of ratification is for three-fourths of states must vote in favor of the amendment during a ratifying convention. This alternate method has only been used one time, for the ratification of the Twenty-First Amendment which repealed Prohibition.
Two-thirds
51%
Three fourths.
Not only Congress needs to approve a change, but the states must also approve.
To ratify a new amendment, the proposed amendment has to be approved by 2/3 of both houses of congress before it is approved by 3/4 of the state legislatures or by 3/4 of the states in special conventions convened specifically to debate and decide on the proposal
3/4 of the legislatures of each state or ratifying conventions of each state, as Congress so directs, is needed to approve an amendment to the US Constitution.