What is a backup offer on a house? A fully signed contract in second position that becomes the deal automatically if the first one ends, at no cost to the buyer until it does.
A backup offer is a complete purchase contract, signed by both sides, with an addendum saying it takes effect only when the first contract terminates. It is not a note on file and it is not a promise to consider someone later. Until the first deal ends the backup buyer owes nothing: no earnest money is deposited, no inspection clock runs, and the addendum normally lets them withdraw in writing at any time before activation. On the day the first contract is cancelled the backup becomes the contract, the deposit goes to escrow, and the contingency periods start from that date.
Sellers take them because first buyers do not always finish. Between the inspection, the appraisal and the loan approval there is a real fall-through rate, and a seller whose first buyer walks on day twenty is choosing between relisting into a stale days-on-market count and signing a buyer who has already agreed to a price. The status usually stays active under contract while a backup is in place, and some MLSs carry a specific label for it, so a listing that looks taken can still be worth writing on.
The second effect is leverage, and it is worth naming honestly. A seller with a signed backup at a known price treats a large repair request from the first buyer as a choice rather than a threat, which is why some listing agents solicit backups on purpose. The buyer's side of that bargain is the option value: a signed second position on the home they want, held for the cost of a signature. Kouzr's listing pages keep their own daily status history, so a home that has already been under contract once and come back is visible rather than buried.
A worked example
A home goes under contract at $455,000 on 6 March and stays active under contract while the inspection and appraisal run. A second buyer signs a backup at $448,000 on 12 March, deposits nothing, and keeps the right to withdraw. On 24 March the first buyer's loan is declined and the contract is cancelled. The backup activates that day: $10,000 in earnest money goes to escrow, the inspection period starts from 24 March, and the seller has not lost a day of marketing time.
Questions people ask
Does a backup offer cost anything?
Normally nothing until it activates. The earnest money is not deposited while the offer sits in second position, and most backup addenda let the buyer withdraw in writing at any time before the first contract ends. What it costs is the commitment to a price agreed before you know whether you will be held to it.
How often do backup offers become the deal?
Often enough that sellers ask for them. A meaningful share of contracts end during the inspection, appraisal and loan-approval windows, so a backup on a home whose first buyer still has all three open is a real position rather than a courtesy.