I think it is every 6 months, my friend says more often.

I start T in a few weeks and here is what my doctor (who is a Professor of Endocrinology at Wake Forest told me). Once I begin I will need my levels checked after 3 months. At that time if I decide to up my dose I will need it again in 3 months. After I reach a dose I am going to stay at then every 6 months to a year is fine and up to me.

I am almost at a year on T and I have mine checked every three months

for 6 months my doc checked monthly, then every three months for 6 months, now is every six months and will be for the long term future.

I've heard every 3-6 months a lot... I have only had mine checked twice in the almost 5 years of being on T, and both times were within a year of starting. I'll probably try to go every 6 months to a year once I get insurance stuff straightened out here soon.