No longer than the buy rates behind it: often to the end of the carrier's rate period for sea freight, and a week or less for air.
Write a date, not a duration, add a cargo-ready condition, and say which lines (surcharges, duty, tax) are charged as applicable at shipment. When a quote expires, refresh it and say what changed.
Full guide: Freight quote validity explained.
State the exact date ("valid until 20 Nov 2026"), not "valid 7 days", and add that rates are subject to space and equipment at booking. Put the quote reference beside it, so when the booking arrives you can match it to the rates you quoted. If the customer books after expiry, re-price before confirming rather than honouring a rate you no longer hold.
A rate sheet with a "valid to" date on every rate makes this automatic: the quote can never be valid longer than the cheapest line on it.
Laneworks drafts the reply to a quote request from your own rate sheet in about two minutes. Forward a real request to try@getlaneworks.com to see it on your own work.