Offer and acceptance in contract law is the two-step exchange that creates a binding agreement: one party proposes definite terms, and the other agrees to them without changes. American courts judge both steps by an objective standard, which means your private intentions don’t control. What matters is how a reasonable person would read your words and conduct. Get the exchange right and you have a contract. Get it wrong, and what felt like a deal may be nothing at all.
What Makes a Proposal a Legal Offer
An offer is a communication that would lead a reasonable person to believe they can say “yes” and close the deal on the stated terms. The Restatement (Second) of Contracts calls it a “manifestation of willingness to enter into a bargain” made so the other side is justified in thinking their agreement will finish things.
Three elements have to be present:
- Definite terms. The proposal has to be specific enough that both parties understand what’s being exchanged and on what conditions. “I might sell my car someday” isn’t an offer.
- Apparent intent to be bound. The person proposing must look willing to be locked in if the other side agrees. A joke at a dinner party doesn’t qualify, even if the words describe a transaction.
- Communication to the offeree. The offer has to reach the person it’s aimed at. You can’t accept a deal you don’t know exists.
The intent requirement is where the objective standard does its heaviest lifting. You might privately believe you’re bluffing when you offer to sell your truck for $8,000, but if your outward signals would convince a reasonable person you meant it, a court can hold you to it. What’s inside your head doesn’t matter when the words and behavior point the other way.
Advertisements and Price Tags Usually Aren’t Offers
Not everything that looks like an offer is one. Store displays, price tags, catalogs, and most advertisements are invitations to negotiate. They invite you to make an offer, not the other way around. When you take an item to the register, you’re the one offering to buy, and the store can decline.
The practical reason is control. If every ad were a binding offer, a seller would be locked into unlimited contracts the moment the ad ran, regardless of inventory. The exception is an advertisement so specific that nothing is left to negotiate: all essential terms stated, performance defined, acceptance possible without further discussion. Those are rare.
What Counts as Acceptance
Acceptance is the offeree’s unqualified agreement to the exact terms of the offer. Under the mirror image rule, any response that adds conditions or changes terms isn’t an acceptance at all. It’s a counter-offer, which rejects the original and puts a new proposal on the table.1Legal Information Institute. Mirror Image Rule
Acceptance can take several forms. Saying or writing “I accept” is the clearest. Conduct also works: if someone offers to pay you to paint a room and you show up and start painting, your actions communicate acceptance. Either way, the acceptance has to be communicated to the offeror. A private decision to say yes that you never express doesn’t form a contract.2Legal Information Institute. Offer
Silence almost never counts. The narrow exceptions: someone takes the benefit of services they could have refused and knew were offered with the expectation of payment; the parties have a prior course of dealing that makes silence a reasonable signal of agreement; or the offeror has told the offeree that silence will be treated as acceptance and the offeree actually intends to accept that way. Outside those situations, a seller cannot mail you unrequested merchandise and claim your failure to return it binds you to buy.
When Does the Contract Actually Form?
Timing matters because formation determines when rights and obligations lock in. The general rule: a contract forms when the offeror receives the acceptance.
The main exception is the mailbox rule. When acceptance travels through a non-instantaneous medium like postal mail, it takes effect the moment the offeree sends it, not when the offeror receives it.3Legal Information Institute. Mailbox Rule Drop your acceptance letter in the mailbox Monday, and the contract forms Monday even if the letter doesn’t arrive until Thursday. If the letter gets lost entirely, the acceptance is still effective.
One wrinkle catches people out. If you mail a rejection first and then change your mind and send an acceptance, the result depends on which communication the offeror receives first. If the rejection arrives first, there’s no contract, no matter when you mailed the acceptance.
The mailbox rule does not apply to option contracts. When you’re exercising an option, your acceptance must actually reach the offeror to count.3Legal Information Institute. Mailbox Rule An offeror can also override the mailbox rule by stating in the offer that acceptance is effective only on receipt. For real-time communication like phone calls or video conferences, acceptance is effective immediately when spoken.
How an Offer Can End Before Acceptance
Offers don’t last forever. Several things can kill one before anyone accepts:
- Revocation. The offeror can withdraw the offer any time before acceptance, but revocation only works when the offeree learns about it. If you mail a revocation and the offeree accepts before your letter arrives, you have a contract.2Legal Information Institute. Offer
- Rejection. If the offeree says no, the offer dies. They can’t later change their mind and accept it.
- Counter-offer. Proposing different terms rejects the original and replaces it. Once you counter-offer, the original deal is gone permanently.
- Lapse of time. If the offer sets a deadline, it expires when the deadline passes. With no deadline, the offer expires after a reasonable time, which depends on the circumstances. An offer to buy fresh produce has a shorter life than an offer to buy a building.
- Death or incapacity. If either party dies or becomes mentally incapacitated before acceptance, the offer terminates automatically, even if the surviving party has no idea.
- Supervening illegality. If a change in law makes the proposed transaction illegal before acceptance, the offer is extinguished.
Keeping an Offer Open
Because offerors can revoke so freely, offerees sometimes need a guarantee the offer will stay available. There are two main routes.
An option contract is a separate agreement where the offeree pays the offeror something of value in exchange for a promise to hold the offer open for a set period. Real estate deals use this structure often: a buyer pays a few hundred or thousand dollars for a 30-day option to purchase a property. During that window the seller can’t revoke. The option payment is independent of the purchase price and typically non-refundable.
Under the Uniform Commercial Code, merchants get a shortcut called a firm offer. When a merchant makes a signed, written offer to buy or sell goods and states the offer will remain open, that promise is binding without any payment for up to three months. If no duration is specified, the offer stays open for a reasonable time, capped at three months regardless. The rule applies only to merchants, only to goods, and only when the assurance is in a signed writing.
There’s also a protection built in for offers that call for performance rather than a promise. If someone offers to pay you $500 to paint their fence, they can revoke freely before you start. Once you pick up the brush and begin painting, the law implies an option that gives you a reasonable time to finish. The offeror can’t pull out after you’ve started performing.
How the UCC Changes the Rules for Goods
The mirror image rule works cleanly for handshake deals between individuals, but it caused problems in commercial transactions. Businesses routinely exchange purchase orders, invoices, and acknowledgment forms loaded with boilerplate that never quite matches. Under strict mirror image reasoning, these everyday transactions wouldn’t form contracts because the paperwork was always slightly different.
The UCC, which governs the sale of goods in all 50 states, addressed this with Section 2-207. A response that adds or changes terms can still operate as a valid acceptance, as long as it’s a definite expression of agreement sent within a reasonable time. The additional terms are treated as proposals. Between merchants (businesses that regularly deal in the goods at issue), those additional terms automatically become part of the contract unless they would significantly alter the deal, the original offer expressly limited acceptance to its own terms, or the other side objects within a reasonable time.
If you buy or sell goods in a business context, don’t assume the mirror image rule applies. The UCC’s more flexible standard likely controls.
Clicking “I Agree” Online
When you click “I Agree” on a website, you’re engaging in contract formation backed by federal law. The Electronic Signatures in Global and National Commerce Act (ESIGN) provides that a contract can’t be denied legal effect solely because an electronic signature was used.4Office of the Law Revision Counsel. 15 USC 7001 – General Rule of Validity An electronic signature can be anything from typing your name in a form to clicking a clearly labeled “Accept” button, as long as you intend the action to signify agreement.
Courts draw a sharp line between two online formats. Clickwrap agreements require you to click a button or check a box confirming agreement before you can proceed. Courts routinely enforce these because clicking is an affirmative act of acceptance. Browsewrap agreements bury terms behind a hyperlink at the bottom of the page and assume you’ve agreed by using the site. Courts are much more skeptical. Unless the site gave conspicuous notice of the terms and you took some clear action showing agreement, a browsewrap agreement may not hold up.
The practical lesson works both ways. If you want a digital agreement to stick, require an affirmative click. If you’re a consumer, clicking “I Agree” creates real legal obligations even when you skip the fine print.
Why Consideration Still Has to Be There
A clean offer and acceptance won’t produce an enforceable contract on their own. The deal also needs consideration: something of value exchanged by both sides.5Legal Information Institute. Consideration Consideration is what separates a binding contract from a gift or a gratuitous promise.
Consideration doesn’t have to be money. It can be a promise to do something, a promise to refrain from doing something, or the actual performance of a service. What matters is that each side gives up something or takes on an obligation they didn’t have before. A promise to give someone $5,000 with nothing expected in return is a gift. A promise to pay $5,000 in exchange for painting a house is a contract, because both sides have assumed obligations.5Legal Information Institute. Consideration
Courts rarely second-guess whether the price was fair. A lopsided deal is still enforceable as long as both sides exchanged something of value. Only extreme disparity might prompt a court to look at whether fraud or duress tainted the agreement.5Legal Information Institute. Consideration
One trap worth knowing: past consideration doesn’t count. If your neighbor mows your lawn uninvited and you later promise to pay $50 for the work already done, that promise usually isn’t enforceable. The mowing happened before the promise, so there was no bargained-for exchange at the time of the agreement.
When a Verbal Deal Isn’t Enough
Most contracts don’t have to be in writing. A verbal agreement with offer, acceptance, and consideration is legally binding. But a few categories must be memorialized in a signed writing under the statute of frauds. Without one, these are unenforceable even if both sides agree the deal happened:
- Contracts for the sale or transfer of an interest in real property, though short-term leases under one year are often exempt.
- Agreements that by their terms cannot be performed within one year from the date they’re made.
- A promise to pay someone else’s debt (suretyship).
- Contracts for goods priced at $500 or more, under UCC Section 2-201.
- Promises made in consideration of marriage, such as prenuptial agreements.
- A promise by an estate executor to pay estate debts from personal funds.
The writing doesn’t need to be a formal contract. An email, a signed letter, or a text message can satisfy the requirement as long as it identifies the parties, describes the essential terms, and is signed by the person being held to it. Under the ESIGN Act, an electronic signature satisfies the statute of frauds for most commercial transactions.4Office of the Law Revision Counsel. 15 USC 7001 – General Rule of Validity The writing exists to prevent fraudulent claims about oral agreements in high-stakes deals, not to add formality for its own sake.