The short answer
Four months on a conventional loan before the appraiser has to update it and twelve months at the outside, 180 days on an FHA loan, and six months on a VA loan for an existing home; the clock starts on the appraisal's effective date, and it is the loan program's rule rather than anything about the house.
Nothing expires about the appraisal itself. What carries a date is the lender's willingness to rely on the value, and each loan program sets that date differently. The question usually comes up in one of three situations: a purchase that has dragged on, a new-construction home that will not be finished for months, or a buyer who has changed lenders and wants to know whether the report they already paid for moves with them.
The three clocks
On a conventional loan sold to Fannie Mae, the appraisal has to be no more than twelve months old at the note date, and once its effective date is more than four months old the appraiser has to complete an update: an exterior inspection and a review of current market data confirming the value has not declined. Past twelve months, with or without an update, the lender orders a new appraisal.
FHA sets a single 180-day validity period from the effective date, which replaced the older 120 days plus a 30-day extension in 2022, and an update extends it to one year from that original date. VA notices of value are good for six months on an existing home and twelve months on one that is proposed or under construction, and where the buyer signs a purchase agreement while the notice is valid it stays valid for that transaction until it closes or dies.
In all three the effective date is the day the appraiser inspected, not the day the report arrived or the day the lender read it, and that is often a week earlier than people assume.
What an update actually is
An appraisal update is a short form completed by the original appraiser, exterior rather than interior, stating whether the market has declined since the original effective date. Where the program allows it and the appraiser is available it is cheaper and faster than a new report: a fraction of the original fee and a few days. If the appraiser concludes the value has declined, the update becomes a new appraisal at the lower number, which is the risk in leaning on one.
The same short form covers a completion report, which is what confirms that repairs the appraisal required, or construction that was unfinished at inspection, are done.
It was ordered for one lender and one deal
The appraisal is prepared for the lender that ordered it, and on a conventional loan its transfer to a different lender is at the two lenders' discretion rather than the borrower's right. In practice a buyer who changes lenders mid-escrow pays for a second appraisal, and that is one of the real costs of switching late for a slightly better rate.
FHA is the exception. The appraisal is attached to the FHA case number on the property, and when a borrower moves to a different FHA lender the first lender has to transfer the case number and the appraisal with it at the borrower's request. The value also stays with the property for the rest of its validity period, so a second FHA buyer inherits a low appraisal on the same house rather than getting a fresh look at it.
Where the dates bite here
New construction is the common case in the valley. A home bought from a builder off a floor plan can be a year from contract to completion, so the appraisal is done early against plans and specifications and then updated or redone before funding, and the upgrades chosen along the way are part of what changes the number. The other case is a probate or trust sale that stalls for months and then comes back, needing an update on a report everyone had stopped thinking about.
Questions people ask
Does an appraisal expire if the sale falls through?
The report does not stop being valid, but it was ordered for one lender and one transaction. A new buyer's lender orders its own on a conventional loan, while on an FHA loan the value stays attached to the property's case number until the validity period runs out.
How long is an appraisal good for on a refinance?
The same clocks apply, because it is the loan program that sets them: four months before an update on a conventional refinance and twelve months at the outside. Many refinances need no appraisal at all, where the lender's automated valuation accepts the property.
Can you use an old appraisal for a new loan?
Only inside the program's window, and only if the new lender will accept a report addressed to somebody else, which conventional lenders generally will not. An appraisal ordered privately for a divorce, an estate or a tax appeal is almost never usable for a mortgage.