The present continuousThe aspect expressing duration, formed with be + verb-ing. E.g.: What are you doing? tenseA grammatical category that is marked by verb inflection. To express when an event or action happens in time or when a state exists, we use tenses. can express fixed social or travel arrangements and plans for the future. Note that you need to use a time expressionA word or group of words used in a particular situation. E.g.: Good morning, at six, on the sofa or some reference to future, otherwise the sentence would refer to present time.

"What are you doing tonight?" "I'm visiting my grandmother.'
I'm travelling to Bratislava in two weeks' time.
My sister is leaving tomorrow.

Diagrams

Present simple to express future
Future time Other structures expressing future