How to Pass a Constitutional Amendment

Article V of the United States Constitution describes the process whereby the federal Constitution may be altered. 

Amendment proposals may be adopted and sent to the states for ratification by either:

A two-thirds vote of members present—assuming that a quorum exists—in both the Senate (A Supermajority 67) and the House of Representatives (A Supermajority 292) of the United States Congress

Or

A two-thirds (A Supermajority 34) vote of a National Convention called by the U.S. Congress at the request of the Legislatures of at least two-thirds (34) of the states. This method has never been used before and would open the floodgate door to an array of additional constitutional amendments favored by a variety of special interests.  The whole process has the potential of making the convention a circus. All thirty-three amendment proposals that have been sent to the states for ratification since the establishment of the Constitution have come into being via the Congress. State legislatures have however, at various times, used their power to apply for a national convention in order to pressure Congress into proposing a desired amendment.

To become an operative part of the Constitution, an amendment, whether proposed by Congress or a National Constitutional Convention, must be ratified by either: The legislatures of three-fourths (38) of the states; or by the State ratifying conventions in three-fourths (38) of the states.

Congress has specified the state legislature ratification method for all but one amendment. The ratifying convention method was used for the 21st Amendment which became part of the Constitution in 1933.

Since the turn of the 20th century, amendment proposals sent to the states for ratification have generally contained a seven-year ratification deadline, either in the body of the amendment or in the resolving clause of the joint resolution proposing it. The Constitution does not expressly provide for a deadline on the state legislatures' or state ratifying conventions' consideration of proposed amendments.

An amendment becomes operative as soon as it reaches the three-fourths of the states threshold. Then, once certified by the Archivist of the United States it officially takes its place as an article of the Constitution.