I can be counted upon to finish what I start.

[xiaoen]

Hello,

I can be counted upon to finish what I start.

I think the above blue sentence is not really natural. What's the natural way to say the above sentence?
In the blue sentence I want to say that I really care for my job.

 

[GoesStation]

Counted on would be more natural, but it's not unacceptable as is. (We don't use "upon" very often.)

You could say I always finish what I start. That statement probably isn't literally true because occasionally outside forces intervene to make finishing something impossible, but saying I always try to finish what I start​ doesn't sound very positive.

 

[tzfujimino]

I can be counted upon to finish what I start.

Does it have to be in the passive?
The active sounds OK to me:
You can count on me to finish what I start.

 

[xiaoen]

but it's not unacceptable as is.

Excuse me, I didn't understand your meaning here. What do you mean?

 

[Rover_KE]

'...it's not unacceptable' means 'it is acceptable, but with some reservations and is not completely and irrefutably acceptable'. (GoesStation's slight demurral concerns 'upon'.)

 

[GoesStation]

Excuse me, I didn't understand your meaning here. What do you mean?

"As is" means as you wrote it in this context. In general it means "in its current state or condition".