Difference between volitional +と思う and volitional+ と思っている


I've looked around the site for anything related but i couldn't find any
clues.

My take at it is that using the volitional form with と思う you're expressing
your plans in the near future as in

> 今晩は薬を飲んで早く寝ようと思います。

you think you'll take your medicine then fall asleep probably said on the same
day or even a few hours before doing the action.

whereas volitional form + と思っている you're expressing your plans probably a few
years in the future

> 来年、フルマラソンに挑戦しようと思っている。

you're thinking about taking on the challenge of a full marathon next year and
probably saying that you've been thinking of taking on the challenge is
correct too because you're still thinking, probably haven't even started
preparing for it or probably even still considering it?

I'm not really sure about this, it's just a speculation, is part of what i
said correct?




In my understanding...

  * ...しようと思う

"I think I will...", "I'll probably..." ( _not fully decided,_ 予想している)

  * しようと思っている

"I'm thinking of...", "I'm planning to..." ( _more-or-less decided,_ 仮に計画している)

> 留学 **しようと思います**

  * **I think I'll** study overseas.

> 留学 **しようと思っています**

  * **I'm thinking of** studying overseas.




In my understanding...

  * ...しようと思う

"I think I will...", "I'll probably..." ( _not fully decided,_ 予想している)

  * しようと思っている

"I'm thinking of...", "I'm planning to..." ( _more-or-less decided,_ 仮に計画している)

> 留学 **しようと思います**

  * **I think I'll** study overseas.

> 留学 **しようと思っています**

  * **I'm thinking of** studying overseas.

