No law sets how long a seller has to sign an addendum. The deadline is whatever the addendum itself states, and buyers typically write in a window of 24 to 72 hours. Until the seller signs, the addendum has no legal effect, and the original purchase agreement stays fully in force.
Why There’s No Fixed Timeframe
A signed purchase agreement is already a binding contract. When a buyer sends over an addendum proposing changes — repair credits after an inspection, a price adjustment following an appraisal, a new closing date — that document works like a fresh offer stacked on top of the existing deal. It proposes different terms and needs new signatures from both sides before it means anything.
Because it’s an offer rather than a mandatory step, the seller is under no obligation to sign it, respond to it, or even acknowledge it. The addendum doesn’t pause the contract. It doesn’t override any deadlines. It doesn’t buy the buyer extra time. Every obligation in the original agreement keeps running while the seller decides what to do.
Setting the Deadline in the Document
Since no statute prescribes a response window, whoever drafts the addendum controls the clock by writing an expiration clause directly into it. Language like “This addendum is null and void if not signed by all parties by 5:00 PM on July 18, 2026” is clear, leaves no room for argument, and gives the seller a firm target.
Most buyers set deadlines between one and three business days, though the right window depends on what’s being proposed. A minor repair request might warrant 24 hours. A significant price renegotiation after a bad appraisal might justify 72 hours so the seller can consult their agent or attorney. The addendum should specify both a date and a time, and a time zone if the parties are in different locations.
What Happens Without a Deadline
If the expiration clause is left out, general contract principles say the offer stays open for a “reasonable” period. That sounds flexible, but it creates problems. What counts as reasonable is vague and fact-dependent, and no one wants to argue about it later. A stated deadline eliminates the ambiguity entirely.
Making the Deadline Strict
Adding a “time is of the essence” clause signals that the stated deadline is absolute and that missing it counts as a material failure. Without that language, courts in some jurisdictions treat deadlines in real estate contracts as aspirational rather than firm. Including the phrase removes the wiggle room: if 5:00 PM Friday is the deadline, 5:01 PM is too late.
Electronic signatures count. Under the Electronic Signatures in Global and National Commerce Act, a signature or contract cannot be denied legal effect solely because it is in electronic form.1Office of the Law Revision Counsel. United States Code Title 15 Section 7001 – General Rule of Validity A seller who signs from their phone at 4:58 PM has signed just as validly as with a pen. Platform timestamps become critical evidence if a dispute arises over whether the signature landed before the cutoff.
What Happens When the Deadline Passes
If the expiration date and time arrive without the seller’s signature, the addendum is dead. It cannot be accepted later unless both parties agree to revive it with a new document. The seller doesn’t have to do anything affirmative to reject it. The clock running out handles that automatically.
Critically, the seller’s failure to sign does not kill the underlying deal. The original purchase agreement remains fully binding. Both parties still owe each other everything the original contract requires. This catches some buyers off guard: sending an addendum and having it ignored doesn’t give the buyer a free exit from the transaction.
The Seller’s Three Options
Once the addendum lands in the seller’s inbox, there are three possible responses.
Accept
The seller signs the addendum as written before the expiration deadline. It then becomes a binding part of the purchase agreement, and both parties are held to the new terms alongside the original ones.
Reject
The seller can say no outright, either by sending a written rejection or by simply letting the deadline expire. Either way, the proposed changes die and the original contract continues unchanged. A written rejection is cleaner because it removes doubt, but silence past the deadline produces the same legal result.
Counter
The seller can modify the buyer’s proposed terms — agreeing to some repairs but not others, for instance — sign the modified version, and send it back. This is where buyers get tripped up. A counter-offer is not a partial acceptance. Under longstanding contract principles, it operates as a rejection of the original addendum and creates an entirely new proposal. The buyer cannot later go back and accept the original addendum they sent, because the seller’s counter-offer extinguished it. The buyer must now accept, reject, or counter the seller’s new terms.
If a seller counters with terms the buyer doesn’t like, the buyer can’t simply say “forget the counter, I’ll take my original addendum.” That original proposal no longer exists as something the seller can accept.
Withdrawing the Addendum Before the Seller Signs
Because an unsigned addendum is just an open offer, the buyer can revoke it any time before the seller signs. If circumstances change or the buyer reconsiders, the addendum can be pulled back, and the seller loses the ability to accept it.
The revocation has to reach the seller before the seller signs. If the seller signs at 2:00 PM and the buyer’s revocation email arrives at 2:05 PM, the addendum is already binding. Send the withdrawal in writing and keep proof of when it was delivered.
What the Buyer Can Do if the Seller Doesn’t Sign
A rejected or expired addendum isn’t the end of the road, but the buyer’s next moves depend on why the addendum was sent in the first place.
Proceed With the Original Deal
The simplest path is to move forward under the original contract terms. If the addendum requested minor repairs or a small credit, many buyers decide the house is still worth it and close without the changes.
Submit a New Addendum
Nothing stops the buyer from trying again with different terms. If the seller balked at a $10,000 repair credit, a revised addendum requesting $5,000 might get traction. Each new addendum is a fresh offer with its own deadline, and there’s no cap on how many times the parties can go back and forth.
Exercise a Contingency to Walk Away
This is where the stakes get real. If the addendum was tied to a contract contingency, most commonly the inspection contingency, the buyer may have the right to cancel the entire purchase and recover the earnest money. An inspection contingency typically gives the buyer a window (often 7 to 10 days after the seller accepts the original offer) to review inspection results and decide whether to proceed. If the seller refuses repair requests during that window, the buyer can invoke the contingency to cancel.
The critical detail is the contingency deadline, not the addendum deadline. If the inspection contingency period has already expired, the buyer likely cannot cancel over inspection issues regardless of what the addendum said. Missing that deadline can mean forfeiting the earnest money deposit. Track both clocks independently: the addendum expiration and the contingency expiration. They’re separate deadlines with separate consequences, and confusing them is one of the most expensive mistakes buyers make.