Which sentence is correct?

Both sentences are grammatically correct , but they’re used in slightly different contexts.

1. “I’m going to watch a movie at 8.”

This is the “going to” future. Use it when:

  • You’ve already decided or planned to do something.
  • The plan exists before the moment of speaking.

Example:

  • “I bought tickets earlier, so I’m going to watch a movie at 8.”

2. “I’ll be watching a movie at 8.”

This is the future continuous tense. Use it when:

  • You want to emphasize that something will be in progress at a specific time.
  • It can sound a bit more casual, indirect, or polite.

Example:

  • “Sorry, I can’t call you at 8—I’ll be watching a movie then.”

Key difference (simple view)

  • “Going to” = planned decision
  • “Will be watching” = action in progress at that time

Which one should you use?

It depends on what you want to express:

  • If you’re just stating your plan →
    “I’m going to watch a movie at 8.”

  • If you’re explaining your availability or what you’ll be doing at that moment →
    “I’ll be watching a movie at 8.”

Real-life comparison

  • Friend asks: “What are your plans tonight?”
    → “I’m going to watch a movie at 8.”

  • Friend asks: “Can I call you at 8?”
    → “I’ll be watching a movie at 8.”

Bottom line

Neither is “more correct”—they just highlight different shades of meaning. Use the one that fits your situation.