Grammar fix
I'm running late
say you're behind
A common, casual way to tell someone you're behind schedule and won't be on time.
expressionB1core
Hear it in context
Notice where the phrase sounds natural.
Sorry, I'm running a bit late — I'll be there in ten minutes.
A: Are you nearly here?
B: Not quite, I'm running late — start without me.
Fix the pattern
One small grammar move makes it sound right.
Not: I'm running lately.
Say: I'm running late.
It's the adjective 'late', not 'lately'; 'lately' means 'recently'.