An addition to a will is usually called a codicil.

Basic meaning

A codicil is a short legal document that changes, explains, or adds to what is written in an existing will, without replacing the entire will. In everyday terms, it works like an addendum or amendment to your will.

How it is used

  • It can update beneficiaries, change an executor, or add/remove specific gifts while leaving the rest of the will intact.
  • It is typically signed and witnessed with the same formalities required for a will, and it is stored together with the original will so both are read together.

Codicil vs “addendum”

  • Some articles and lawyers also use the word “addendum” for a simple addition to a will, but in estate-planning law the formal term is codicil.
  • For major changes, many experts suggest creating a new will rather than relying on multiple codicils, to avoid confusion.

TL;DR: An official addition to a will is called a codicil, which is a separate, signed document that amends or supplements the original will.