The term “addendum” is used to describe anything that is added to a document. In terms of the law, an addendum can be additional terms added to a contract that were left out when the contract was initially drafted. Addendums can also be used to correct a mistake, or to add terms to something, as in a lease. To explore this concept, consider the following addendum definition.

Definition of Addendum


  1. Additional material, typically omitted, which is added to the end of a document.


Late 17th century          Latin (addere)

What is an Addendum

The term “addendum” refers to any material that needs to be added to a document after the fact. This material is listed under the heading of “Addendum,” and is usually tacked on to the back of the document as its own separate mini document. An addendum can consist of everything from lease terms, to the correction of a mistake that was not noticed until after the document was signed.

For example, an addendum to a separation agreement often covers visitation schedules for holidays that were not previously listed in the initial visitation schedule. Holidays commonly left out are those specific to a particular culture or religion, often because the attorney drafting the agreement is unaware of the specific holidays the family celebrates. So if, for example, Mom is Jewish, Dad’s attorney will include an addendum to ensure she gets to spend all Jewish holidays with the children, while Dad gets to spend the Christian holidays with them.

Addendums for real estate contracts, on the other hand, contain some of the finer points of the agreement. The meat of these documents is often “boilerplate,” which means that the agreement itself is the same one used in all similar cases.

Boilerplate text may be edited to include the parties’ names and locations, or it may simply be copied and pasted with no changes. Once the more specific details need to be added in, such as the exact payments to be made and when, an addendum is often used to account for these details.

Another great example of an addendum is that which may be included on a contract to manufacture a specific product. The initial contract will probably include the company’s requirements when making products in general for the company. The addendum, however, may elaborate further, laying out exactly which products the company wants produced, and the specific parts and processes to be used in their production.

Once an addendum has been created, it must be signed as if it were a separate document, and attached to the original document. An unsigned addendum may be mistaken for a rough draft or, worse, something fraudulent that is being tacked on at the last minute. A signed addendum confirms that its terms are legitimate, that the parties have accepted them, and that they should be upheld.

Writing an Addendum

When writing an addendum, it should match the same font, margins, and style as that which is in the original contract. The addendum should always be titled as such, and the title should be accompanied by the date on which the addendum is to go into effect.

More important than anything in writing an addendum is to ensure that the terms to be modified are clearly listed. You can introduce a change with a statement like “This contract is to be amended as follows…”, and then include the original line and how it should be modified. For example:

“This contract is to be amended as follows:

On page 5, line 12, the title of ‘Mrs. Anderson’ should be changed to ‘Mr. Anderson.’

You can also play around with styles to emphasize that changes have been made. For instance, you can bold the specific words or terms to be changed, and/or you can use the strikethrough function to show what the original term was, and how it is now being struck in favor of the change.

Mutual Assent

In order for an addendum to be considered valid, it must have mutual assent. When mutual assent has been reached, this means that all of the terms have been clearly communicated to the parties, and that they are in agreement with everything in the contract. If there are any elements of the contract that have not been discussed with the parties, or if there is anything the parties cannot agree on, then there is no mutual assent.

Amendment vs. Addendum

If a change needs to be made to a contract, why not just amend the contract? Why the need for an addendum? The difference between an amendment vs. an addendum is that an amendment is a small change that is made to the body of the document. For instance, if the car referred to in a lease agreement is a Honda, but the car is actually a Hyundai, then the contract would be amended to change “Honda” to “Hyundai” throughout.

An addendum, on the other hand, adds a full document to the already existing document. An example of an addendum being used would be if the parties wanted to add something to the original document. For instance, an individual who is purchasing a house may not want to purchase all of the furniture that is being left behind. However, after thinking about it further, he changes his mind. An addendum would then be drafted to include the furniture he is purchasing, and any additional charge(s) for that furniture.

Another difference between an amendment and an addendum is that the person(s) who originally signed the contract are the only ones who can make changes (amendments) to it. An addendum, on the other hand, can be added by an outsider, like an attorney. An amendment is also considered to be part of the contract until the contract is up for negotiation again. An addendum, however, is a legally binding arm of the contract.

Consents and Waivers

When an addendum is created, this is a way of editing the contract without voiding it entirely. You can waive a section of the contract or consent to a minor change without altering the substance of the entire contract. In fact, consents and waivers are ways to show that the parties voluntarily agree with the changes that are being made. In some cases, the parties can even use consents and waivers as a method of agreeing to a breach of the contract, depending on the situation.

Take, for example, a renter’s agreement. A landlord includes a clause in the agreement stating that the tenant must move out by the first of the month after one year. However, the landlord may make an exception if his tenant is having difficulty finding another place to live. He may extend the time to the 15th of the month to give his former tenant enough time to find a new place, rather than throwing him out on the street. He may choose to memorialize this change as an amendment to the contract, or the parties may simply agree to the extension verbally.

Addendum Example Involving a Rental Property

An example of an addendum being contested in a court of law can be found in the case of Gennarelli v. Cherkovsky, which was decided in 2017. Here, Albert Gennarelli rented a property to Iury Cherkovsky in Bellmore, New York for about a year. Once the year was up, Cherkovsky stayed in the house on a month-to-month basis. Allegedly, Gennarelli served Cherkovsky a 30-day notice of termination, which ended Cherkovsky’s tenancy in February of 2017.

Cherkovsky filed a petition to contest the termination of his tenancy and included a copy of the lease and its addendum. Listed in the addendum was the following term:

“After one year period Tenant can remain in the house as long as Tenant needs, Tenant must be offered a renewal of the lease by Landlord.”

Cherkovsky claimed he was never offered a renewal lease, and that Gennarelli admitted to never offering him one. Cherkovsky claimed that, in not offering him a renewal lease, Gennarelli violated the lease.

The District Court of Nassau County ultimately decided that this term of the lease was not enough to enforce a contractual obligation upon Gennarelli. This was because there were more specific details that needed to be included which weren’t, such as the price that Cherkovsky was expected to pay, and the length of the lease.

Specifically, the Court wrote:

Real Property Law §232-C provides that a tenant becomes a month-to-month tenant after expiration of the lease, by the landlord accepting rent unless the agreement provides otherwise. In [this case], Respondent became a month-to-month tenant after Petitioner stopped extending the lease for a year. There is no language in paragraph 8 of the Lease Addendum providing for a further extension of the lease beyond a month by Petitioner accepting rent.

Finally, this court finds that Petitioner offered Respondent a renewal lease, and thereby satisfied paragraph 8 of the Addendum.”

Related Legal Terms and Issues

  • Contract – An agreement between two or more parties in which a promise is made to do or provide something in return for a valuable benefit.
  • Lease – A kind of contract whereby one party provides land or property to another for a specific length of time and in return for payment.
  • Petitioner – The individual who initiates legal proceedings by filing a petition, also referred to as “plaintiff” in some cases.
  • Respondent – The individual against whom a petition is filed, also referred to as “defendant” in some cases.
  • Separation Agreement – An agreement that is made between spouses who are legally separating, but who are not divorcing.