Learn English – Why “on the house” not “in the house”, in “have a dessert on the house”

prepositions

I thought it was a typo but said I should check it on Google, and here you go!

My husband ordered the snapper special grilled and thought it was very
good. The garlic cheddar mashed potatoes are also very good.

Once we were done, our waiter came over and told us that since we had
to wait so long for our food that we could have a dessert on the
house so we got the key lime pie which was good. Overall, we would
return.

I am confused. Is it an idiom? Why "on the house"?

Source: from a comment in a review entitled “Great Food and Atmosphere”

Best Answer

on the house (Cambridge dictionaries online)
If you have something on the house, it is given to you free by a business

It's on rather than in because the idiomatic usage is nothing to do with physical location (for which contexts in is more common in general). It's more a matter of on whose shoulders does the burden of cost fall?, or on whose bill does that cost appear?. The usage also commonly appears in forms like...

"Let's have another drink! This one's on me!". (i.e. - I will pay for it)

OP's on the house effectively combines two idiomatic usages - where on X means cost to be borne by X, and the house is the commercial establishment currently providing your food / drink / entertainment.

Note this closely-related idiomatic usage where the choice of preposition is rather less fixed...

They live on/off State benefits (US: on/off welfare)

Both AmE and BrE favour on in the above, but off is also quite common. Some native speakers may always use one or the other preposition in such constructions, and some may see them as synonymously interchangeable. But to me at least, on there carries more "neutral" implications of a low level of income, whereas off is a more "loaded" usage (implying criticism of people who can't/won't fend for themselves).

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