To write an addendum to a will, draft a short document (called a codicil) that identifies the original will by date, states each change in precise language, reaffirms the rest of the will, and then sign it in front of two disinterested witnesses using the same formalities your state requires for a will itself. Get any of those pieces wrong and the amendment can be unenforceable, leaving your original will to control as written.
The legal name for this document is a codicil. Lawyers and courts use that term; “addendum” is the plain-English version of the same thing.
When an Addendum Fits, and When It Doesn’t
A codicil works best for a single, targeted change. Replacing your executor, correcting a beneficiary’s legal name after a marriage, adding a specific gift of jewelry or a bank account, or removing a bequest to someone who has died are all good candidates. The common thread is that the change is narrow enough that a reader can hold the original will and the codicil side by side and understand both without confusion.
A new will is the better choice when you need to restructure how your estate is divided, when a major life event like divorce or the birth of a child reshapes your priorities, or when you already have one codicil in place and find yourself wanting another. Stacking amendments forces your executor and the probate court to reconcile every change against the original, which slows probate and creates openings for disputes. Estate attorneys often find that drafting a fresh will costs about the same as preparing a codicil, so the apparent savings can be illusory. When in doubt, start over.
What the Document Should Contain
Title and Identification
Open with a clear title: “First Codicil to the Last Will and Testament of [Your Full Legal Name].” The first paragraph should identify you by name, state your county and state of residence, and reference the exact date you signed the will you are amending. That ties the codicil to the right document, which matters if you have ever executed more than one will.
The Changes Themselves
Spell out each amendment in specific, unambiguous language. Reference the exact article, section, or paragraph of the original will you are changing. A clean approach: “I revoke Article III of my will and replace it with the following…” followed by the new language in full. Avoid vague instructions like “I want my nephew to get more.” The court needs to know precisely what you are replacing and what replaces it.
Reaffirmation of the Rest of the Will
After listing the changes, include a statement confirming that the rest of your will remains in effect. Something close to: “I confirm and republish my will in all respects other than those changed by this codicil.” Without that clause, an ambiguity could leave a court guessing whether you meant to revoke provisions you never intended to touch.
Capacity Declaration
Most well-drafted codicils include a line affirming that you are of sound mind, acting voluntarily, and free from outside pressure. Testamentary capacity means you understand what property you own, who would naturally inherit from you, what the codicil does, and how those pieces fit together. The language will not stop a challenge on its own, but it creates a contemporaneous record of your mental state that carries weight if someone later contests the document.
Signing and Witnessing
A codicil must be executed with the same formalities your state requires for a will. In nearly every state, that means three things: the document is in writing, you sign it (or direct someone to sign on your behalf in your presence), and at least two witnesses watch you sign and then sign the document themselves. A handful of states have minor variations, but two-witness execution is the dominant standard.
Choose witnesses who are “disinterested,” meaning they do not stand to inherit anything under your will or codicil. In states that follow the Uniform Probate Code, an interested witness will not automatically invalidate the document, but many other states will void the gift to that witness or limit it to what the witness would have received without the will. The safe practice everywhere is to pick two adults with no financial stake in your estate.
Most states also allow a self-proving affidavit, which you and your witnesses sign under oath before a notary public at the same time you execute the codicil. The affidavit works as pre-authenticated testimony that the signing followed proper procedures. During probate, the court can accept the affidavit instead of calling your witnesses to appear and testify. Notary fees are typically modest, and the time saved later is well worth it.
Handwritten Addendums
Roughly half of U.S. states recognize holographic wills, and that recognition generally extends to codicils. A holographic codicil is one written entirely in your own handwriting and signed by you, with no witnesses required. If you live in a state that accepts them, a handwritten amendment can be valid even without the formal signing ceremony.
The catch: handwritten documents invite more challenges. Handwriting can be disputed, intent can be unclear, and without witnesses no one can testify about your mental state when you wrote it. Even where holographic codicils are permitted, the witnessed-and-signed process gives your changes the strongest footing. Treat a handwritten version as a stopgap, not a first choice.
Storing It and Telling Your Executor
Attach the signed codicil directly to your original will and store them together. A fireproof safe, a safe deposit box, or your attorney’s office all work. The critical point is that a separated codicil might never be found. Every codicil must be submitted to probate alongside the will; if your executor does not know it exists, your estate gets administered under the old instructions and your changes are lost.
Tell your executor where the codicil is stored and that it exists. If you have named a new executor in the codicil itself, make sure that person knows too.
Changing or Revoking the Addendum Later
You can revoke a codicil in three ways. First, execute a new will that expressly revokes all prior wills and codicils, which is the cleanest option. Second, execute a new codicil or written declaration that specifically revokes the earlier one, as long as the new document meets the same execution formalities. Third, physically destroy the codicil by burning, tearing, or obliterating it with the intent to revoke it.
Two things to keep in mind. Revoking your entire will automatically revokes every codicil attached to it. And a new codicil that contradicts an earlier one without expressly revoking it controls only to the extent of the inconsistency; everything in the earlier codicil that does not conflict stays in effect. That kind of layered ambiguity is exactly why most estate planners recommend starting over with a new will rather than piling codicil on codicil.
How Addendums Get Challenged in Probate
A codicil can be contested on the same grounds as a will. The three most common challenges are improper execution, lack of testamentary capacity, and undue influence. Improper execution means the document was not signed or witnessed correctly, and it is the easiest challenge to prevent by following your state’s requirements carefully. A capacity challenge argues you were not mentally competent on the signing date, and it comes up most often when the testator was elderly, ill, or medicated. Undue influence means someone pressured or manipulated you into making the changes; courts look especially closely when a person in a position of trust, such as a caregiver, benefited from the amendment. The person alleging undue influence bears the burden of proving it.
The capacity declaration, disinterested witnesses, and self-proving affidavit discussed above are the first line of defense against all three.