עַל חֶשְׁבּוֹן הַבַּיִת

In English we just say on the house to invite someone to partake in goods free of charge. Hebrew gets more specific, with על חשבון הבית – literally, on the house’s account.

For example

צ’ייסרים היום על חשבון הבית!

Chasers on the house today!

חשבון means not only account, but also arithmetic.