The Constitution can be amended if two-thirds of the House of Representatives and the Senate vote for the amendment and three-fourths of the state legislatures ratify it. The Constitution can also be amended if two-thirds of the state legislatures call a convention and three-fourths of the state legislatures ratify it.
Article V of the U.S. Constitution provides the procedure for the introduction and ratification of amendments. The first way to propose an amendment is to get the two-thirds supermajority vote of the Senate and the House of Representatives. This process does not require the president’s signature. Amendments can be sent to the states for ratification.
Alternatively, in order to initiate an amendment, two-thirds of the state legislatures can request that Congress calls a national convention specifically for this purpose. Amendments can be ratified in one of two ways. In the first method, amendments are ratified if three-fourths of the state legislatures accept it. The second method involves getting the ratifying conventions in three-fourths of the states to approve it. This second method was used once to ratify the 21st amendment, which repealed Prohibition.
According to the Supreme Court, ratification must come within a reasonable time after the amendment has been proposed. Starting with the 18th amendment, Congress has typically set a definite period for ratification. In several cases, including the 18th and 20th amendments, the reasonable period set was 7 years. It has not been established how long a reasonable time may extend.