Both kick in and kick off are commonly used in everyday conversation, but kick off is slightly more common. This is because it's used for various activities such as starting a game, a meeting, or a party. Kick in is used less frequently and is mainly used when we're talking about the start of a process or the effects of something.

Both kick in and kick off are informal phrases used in casual conversations. They are suitable for everyday interactions with friends and family. However, in more formal settings like business or academic contexts, using alternative expressions can convey a more polished tone.

The tone of kick in and kick off can differ based on context. Kick in often carries a sense of anticipation or relief when referring to the start of a process or the effects of something. In contrast, kick off typically has an energetic and enthusiastic tone, especially when referring to starting an event or activity.