It's a long acting test...I'm not sure of the exact half-life. If you are refferring to oral test undeconate (andriol) don't bother with it. I don't think it's available as an injectable.
BTW, when I said I don't think it's available as an injectable...I meant alone. It is found in sust/omna etc. If you are stuck with andriol, there is a thread in the archives that tells you how to make it into an injectable. My first "cycle" was andriol only....I was a newbie and I mistook andriol from anadrol...I thought I was going to get huge....I gained about 2 pounds