Passer par pertes et profits means something like accept that you have taken a loss and continue without mourning it, it has a sure accounting flavor. I think write off would be the correct term in English.

Passer quelquechose par pertes et profits literally means “to write something in the balance sheet”, or in the “profit and loss account sheet”.

This means you accept a loss or failure and you admit you can’t do anything about that, or that the problem is not worth the effort needed to solve it. So you have to move on.

It’s still in use in the accounting language, and the proper translation would be “to write off”.

I think I could answer, being an “Expert-comptable” in France = Chartered Accountant in UK.

Ordinary gains (e.g. what you sell) and expenses (e.g. what you buy) go to the “compte d’exploitation”.

But you may have an unexpected loss (some parcels of goods being destroyed by accident, etc.), or profit (a debt you cancelled in your books, having no more hope to recover it, and the written as “pertes” on the previous year, but is finally settled) ; they go to the “Compte des Pertes et Profits”.

The first case unfortunately happens more often, since the general meaning “too bad, forget it”.