ごちそうさまでした。

Gochisōsama deshita.

Thank you for the meal. (after eating)

Word for word

“It was a feast.”

Politeness: Polite

です/ます style. The safe default with strangers, shop staff and colleagues.

When you would say it

When you finish, and as you leave a restaurant.

Worth knowing

Casual: ごちそうさま。 Say it to staff as you go out; it is not just for the person who cooked.