Is tutoring (outside university) while doing PhD a good idea? Just to ask some advice regarding tutoring students while pursuing a PhD to supplement my income.
Is this a good idea? Tutoring pays well in my country, and I am intending to teach twice a week(2 hours each), which would generate a side income equivalent to 30% of my stipend.

(Side info: I am researching Mathematics)

Thanks for your advice!
Of course, whether it is a good idea can only be known in hindsight. But many PhD students work as private tutors, so if it sounds interesting to you, you might as well try it.

Some things to consider:


It will probably take you some time to prepare for each lesson. And unless your students will come to your home or office, also account for travel time and expenses. Four hours of lessons per week may require significantly more than four hours of your time.
What will you do if your students are late to their lesson, or don't show up at all? What if they don't study for their lessons? What if they are late in paying you? What if they (or their parents) demand some different style of tutoring than you had planned? What if they demand that you just do their homework while they Facebook?
Consider the time it will take you to recruit students. Assume that they  will quit unexpectedly, requiring you  to find new students and lose income in the meantime. Do not count on your tutoring fees as steady income.
Ethical issues: if you are working as a teaching assistant or something similar, you cannot be a private tutor to students who are enrolled in your class. Check for other ethics or conflict of interest rules that your university may have. In particular, although your university office may seem like a convenient place to meet your private students, this may not be allowed.