present tense vs present continuous

[kiranlegend]

I plan to play tennis this afternoon

[BobK]

But 'Don't come round this afternoon. I'll be playing tennis.'
And -
'I'm not sure I can come round on Monday. Let me check my diary. I think I'm playing tennis'.

b

[BobK]

Afterthought:

But 'I can never make a meeting on a Monday. I always play tennis then.'

b

[mykwyner]

"I plan to play tennis this afternoon."

The main verb in this sentence is plan, and it is in the simple present. The present continuous would be: "I am planning to play tennis this afternoon." To my ear, the present continuous expresses a slight degree of uncertainty.