YOU SAID:

I'm going for a run today.

INTO JAPANESE

今日は走りに行きます。

BACK INTO ENGLISH

I am going to run today.

INTO JAPANESE

今日走るつもりです。

BACK INTO ENGLISH

I am planning to run today.

INTO JAPANESE

今日は走るつもりです。

BACK INTO ENGLISH

I am planning to run today.