An offer is considered accepted in contract law the moment the offeree communicates unconditional agreement to its terms through a method the offer invites or the circumstances make reasonable. In most distance communications, that moment is when the acceptance is sent, not when the offeror receives it. Pinning down the exact instant matters because it decides when both sides are legally bound and when the offeror loses the power to walk away.
What Makes a Response Count as Acceptance
A response is acceptance only if it matches the offer’s terms without adding, qualifying, or changing anything. Contract law calls this the mirror image rule. Alter the terms and you haven’t accepted; you’ve rejected the original offer and made a counteroffer, which the other side can take or leave.1Legal Information Institute. Mirror Image Rule Once that happens, the original offer is dead and cannot be revived unless the original offeror puts it back on the table.2Legal Information Institute. Counteroffer
Not every modification kills the deal, though. There is a difference between a counteroffer and a mere inquiry during negotiation. “I accept, but could we also add a warranty?” may be treated as acceptance plus a request, depending on the wording. “I accept only if you add a warranty” is conditional, which makes it a counteroffer because the agreement now depends on a new term.2Legal Information Institute. Counteroffer
Acceptance also has to happen while the offer is still alive. If the offer set a deadline, that deadline controls. Without one, the offer stays open for a reasonable period based on the circumstances. And the offeree must actually know about the offer. Someone who independently does what the offer requested, without knowing it existed, hasn’t accepted anything.
How Acceptance Can Be Communicated
Acceptance doesn’t always require a signature or a formal letter. The method just has to fit what the offer invites or what the situation reasonably permits.
Express Acceptance
The clearest form is a direct statement: signing a written agreement, replying “I accept,” or checking a box. There’s little room for ambiguity when the offeree explicitly says yes.
Acceptance by Conduct
Actions can communicate agreement as clearly as words. If someone offers to pay you to paint their fence and you arrive the next morning with brushes and paint, your conduct accepts the offer. The test is whether a reasonable observer would conclude you agreed to the deal.
When Silence Counts as Acceptance
Silence almost never equals acceptance. An offeror cannot force a contract by saying, “If I don’t hear back by Friday, I’ll assume you agreed.” Three narrow exceptions exist under general contract principles:
- The offeree accepts the benefit of offered services, has a chance to refuse, and knows the provider expected payment.
- The offeror said silence would count as acceptance, and the offeree stayed silent specifically meaning to accept.
- Past dealings between the parties have established a pattern where silence reasonably signals agreement, so the offeree is expected to speak up if they want to decline.3OpenCasebook. Contracts – R2K Section 69
Outside these situations, saying nothing creates no contract.
When Acceptance Takes Effect: The Mailbox Rule
Under the mailbox rule (also called the dispatch rule), acceptance becomes effective the moment it leaves the offeree’s possession, not when the offeror receives it. Drop a properly addressed, stamped acceptance letter in the mailbox and a contract exists right then, even if the letter is delayed or lost entirely.4Legal Information Institute. Mailbox Rule
This is the default for ordinary bilateral contracts, and it extends to any communication method the offer invites, including fax and email, so long as the message is irrevocable once sent. The reasoning is practical. Once the offeree sends an acceptance, they’ve committed; forcing them to wait until the offeror confirms receipt would be unfair and commercially impractical.
The rule creates a race between acceptance and revocation. An offeror can withdraw an offer at any time before acceptance, but revocation only takes effect when the offeree actually receives it. So if you mail a revocation on Monday and the offeree mails an acceptance on Tuesday before your revocation arrives Wednesday, the acceptance wins. A binding contract formed on Tuesday.
The Option Contract Exception
Option contracts flip the rule. When an offeree has paid for the right to keep an offer open, acceptance is not effective until the offeror actually receives it.4Legal Information Institute. Mailbox Rule The offeree already has protection against revocation (that’s what they paid for), so the dispatch rule’s rationale doesn’t apply. Hold an option to buy property, mail your acceptance on the last day, and it still has to arrive on time.
When the Offer Overrides the Default
The mailbox rule is a default, not a mandate. An offeror can specify that acceptance is effective only upon receipt, or require a particular method. Language such as “acceptance must be received by June 1” or “acceptance is effective only upon delivery” displaces the dispatch rule entirely.
Acceptance by Performance
Some offers ask for action rather than a promise. “I’ll pay $500 to anyone who finds my missing dog” is accepted by finding the dog, not by promising to look. These are unilateral contracts, and performance is the only way to accept them.
What if someone starts performing but hasn’t finished? Most courts say the offeror cannot pull the offer once performance has begun. Starting the invited performance creates an option contract: the offeror can’t revoke, but they only owe payment if the offeree finishes.5OpenCasebook. Restatement 2d Section 25, 45, and 87 – Option Contracts Merely getting ready to perform doesn’t trigger this protection. Buying supplies for the job isn’t the same as starting the job.
Acceptance in Sales of Goods
The mirror image rule works in simple deals but breaks down in commercial reality. Businesses swap purchase orders, invoices, and confirmations with pre-printed terms that rarely line up. If every mismatch destroyed the deal, most commercial sales would never form a binding contract.
The Uniform Commercial Code, which governs sales of goods in every state, solves this through Section 2-207. A response that expresses acceptance can form a contract even when it contains terms that differ from the original offer.6Legal Information Institute. UCC 2-207 – Additional Terms in Acceptance or Confirmation The additional or different terms are treated as proposals. Between merchants, those proposals automatically become part of the contract unless:
- The original offer required acceptance on its exact terms.
- The new terms would materially change the deal, such as liability caps, warranty disclaimers, or arbitration clauses.
- The offeror objects to the new terms within a reasonable time.6Legal Information Institute. UCC 2-207 – Additional Terms in Acceptance or Confirmation
When both sides act as though a contract exists (shipping goods, making payments) even though the paperwork never aligned, the UCC still recognizes a contract. Its terms are whatever the two sets of forms had in common, filled in by the UCC’s default provisions. Disputes get messy here, because the terms each party assumed were governing may not be the ones that actually control.
The UCC also takes a broader view of acceptance generally. Unless the offer clearly says otherwise, it can be accepted by any reasonable method, and an order for goods can be accepted either by promising to ship or by actually shipping them.7Legal Information Institute. UCC 2-206 – Offer and Acceptance in Formation of Contract
Electronic Acceptance: Clicks and Online Agreements
Most contracts people enter today involve clicking a button rather than signing a page. Federal law treats electronic signatures and records as legally equivalent to paper. Under the E-SIGN Act, a contract cannot be denied legal effect solely because it was formed with an electronic signature or electronic record.8Office of the Law Revision Counsel. United States Code Title 15 Section 7001 The Uniform Electronic Transactions Act, adopted in nearly every state, reinforces the same principle at the state level. Both sides must intend to sign, both must consent to doing business electronically, the signature must be tied to the specific record, and both parties must be able to keep a copy.
Clickwrap Agreements
Clickwrap agreements require you to take an affirmative step, like checking an unchecked box or clicking “I Agree,” before you can continue. Courts routinely enforce these because the deliberate action shows notice and assent. The strongest designs display the terms on screen or link them prominently and require scrolling before the acceptance button activates.
Browsewrap Agreements
Browsewrap agreements are far weaker. These are terms buried behind a small hyperlink at the bottom of a webpage, and they try to bind you merely because you used the site. Courts often refuse to enforce them unless the site can show the user had actual or constructive notice. A faint link in small grey text at the footer usually isn’t enough. Courts look at whether the link was conspicuous (contrasting color, placement near an action the user must take) and whether the user did something that unambiguously showed assent.
The practical takeaway: clicking “I accept” next to clearly labeled terms almost always binds you. Terms simply posted somewhere on a site you happened to visit are a much shakier basis for a contract.
When an Offer Can No Longer Be Accepted
No offer stays open forever. Once it terminates, no amount of agreement on the offeree’s part can bring it back. Offers end in several ways:
- Revocation. The offeror withdraws the offer before acceptance. Revocation must actually reach the offeree to be effective, which is the opposite of how acceptance works under the mailbox rule.
- Rejection or counteroffer. When the offeree says no or responds with materially different terms, the original offer is gone.2Legal Information Institute. Counteroffer
- Lapse of time. A stated deadline controls. Without one, the offer expires after a reasonable period, which depends on context: an offer on perishable goods might last hours, while a real estate offer might survive weeks.
- Death or incapacity. If either party dies or becomes legally incapacitated before acceptance, the offer terminates automatically, regardless of whether the other party knows.
- Destruction or illegality. If the subject of the offer is destroyed, or a change in law makes the proposed transaction illegal, the offer ends by operation of law.
The main exception to revocation is the option contract. When the offeree pays consideration to keep an offer open, the offeror cannot revoke during the agreed period. Under the UCC’s firm offer rule, a merchant who signs a written assurance to keep an offer open is bound by it for up to three months, even without payment.