How do you say free of charge in English?

There are several ways to say "free of charge" in English, depending on the context and desired level of formality. Here are a few options:

Formal:

* Free of charge

* At no cost

* Complimentary

* Without charge

Informal:

* Free

* No charge

* On the house (usually for food or drinks)

* It's on me (usually for food or drinks)

More specific:

* Free shipping

* Free trial

* Free consultation

The best way to choose the right phrase is to consider the context and your audience.