A warranty is a written promise, usually attached to a purchase, to repair or replace a product if it turns out faulty within a set period. A guarantee is a broader firm promise that something will happen or work as described, and does not have to be written down. A laptop comes with a two-year warranty; a company guarantees a full refund if you are not satisfied.
The core difference
A warranty is a specific written promise tied to a product, while a guarantee is any firm promise, written or not.
- warranty — a written promise of repair or replacement within a set period: She sent the broken toaster back under warranty.
- guarantee — a firm promise that something will happen or work as described: There is no guarantee the flight will leave on time.
How to tell them apart
The two words are close cousins. Warranty comes from Anglo-Norman warantie, a variant of Old French guarantie, and guarantee comes from that same Old French root by a different route. That shared ancestry is exactly why they overlap so much in everyday use.
A useful test: if it is a formal document that came in the box with your purchase, it is almost always called a warranty. If someone is simply promising an outcome, such as a refund or a result, guarantee is the more natural word.
