Court has the discretion in deciding whether the jail terms to run concurrently or consecutively.

Normally they will consider a few factors to guide them, whether it is a one transaction, whether such offences are distinct offences, and to look at the sentencing in totality (whether it is excessive).

If John was convicted for 2 drug offences, one packet of drugs found inside his pocket, and another one inside his car on the same day. Normally in such circumstances, it will run concurrently.

If John robbed a lady and subsequently raped her, it is a two separate offence though it was committed in a single transaction, then it is likely that it will run consecutively.

Anyway those are guiding factors only.